QuIC Talk by Swati Chaudhary: Phonons with angular momentum: Magnetic properties and applications

00:52:19
https://www.youtube.com/watch?v=QaFJlnLMhts

Resumo

TLDRSwathi Chaudhary, an accomplished researcher, presents on the angular momentum of phonons, exploring their magnetic properties and applications in materials science. She explains how phonons can exhibit angular momentum and contribute to magnetic moments through mechanisms such as orbital-lattice coupling. The talk outlines various materials where these effects can be observed and emphasizes the potential applications of chiral phonons in electronics, thermal transport, and controlling magnetization using ultrafast technologies. Chaudhary provides a comprehensive overview of theoretical models, experimental results, and the implications of her research for future advancements in the field.

Conclusões

  • 🔍 Phonons can exhibit angular momentum and magnetic moments.
  • 💡 Chiral phonons display unique magnetic properties that can be useful in practical applications.
  • 📊 Orbital-lattice coupling explains how phonons can have significant magnetic moments in certain materials.
  • 🌌 The research opens up avenues for new materials and applications in electronics and thermal transport.
  • 🔬 Magnetic properties of phonons can potentially enhance magnetization control in ultrafast technologies.

Linha do tempo

  • 00:00:00 - 00:05:00

    Introduction of Swathi Chaudhary as the speaker, highlighting her academic journey and experience in quantum information and her current focus on phonons and their properties.

  • 00:05:00 - 00:10:00

    Overview of the presentation on phonon angular momentum, chirality, and its magnetic properties and applications, setting the stage for an in-depth discussion.

  • 00:10:00 - 00:15:00

    Explanation of phonon momentum and how it contributes to phenomena such as chirality in phonons, leading to the exploration of their magnetic moments and mechanisms.

  • 00:15:00 - 00:20:00

    Introduction to a microscopic model for understanding orbital lattice coupling and its implications for magnetic moments in various materials, along with group theoretic aspects.

  • 00:20:00 - 00:25:00

    Definition and significance of angular momentum in photons and phonons, including the derivation of angular momentum from lattice vibrations and potential physical implications.

  • 00:25:00 - 00:30:00

    Discussion on circularly polarized phonons and their interactions with magnetic fields, presenting examples and exploring their unique properties in different materials.

  • 00:30:00 - 00:35:00

    Investigation of mechanisms behind the emergence of substantial magnetic moments in phonons, comparing classical predictions with experimental observations in various types of magnetic materials.

  • 00:35:00 - 00:40:00

    Presentation of a theoretical framework addressing how phonons can couple with electronic states, leading to higher-than-expected magnetic moments observed in experiments.

  • 00:40:00 - 00:45:00

    Consideration of potential applications in electronics, thermoelectrics, and advanced materials, outlining the promise of circularly polarized phonons in device technology and thermal transport capabilities.

  • 00:45:00 - 00:52:19

    Conclusion summarizing the key findings and future directions for research on phonon angular momentum, highlighting the importance of understanding these materials for practical applications.

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Vídeo de perguntas e respostas

  • What is the main topic of the presentation?

    The presentation discusses the quantum properties of phonons, focusing on their angular momentum, magnetic properties, and applications.

  • Who is the speaker and what are her qualifications?

    The speaker is Swathi Chaudhary, who has a BSc from Delhi University, an MSc from IIT Kanpur, and a PhD from Caltech.

  • What are chiral phonons?

    Chiral phonons are phonons that exhibit a circular motion and can carry angular momentum related to the polarization.

  • How do phonons contribute to magnetic moments?

    Phonons can contribute to magnetic moments through mechanisms like orbital-lattice coupling, which allows them to couple with electronic states.

  • What materials are discussed in relation to phonons?

    The discussion touches on various materials with significant phonon behavior, including certain types of magnets and topological materials.

  • What are the applications of phonon angular momentum?

    They can generate effective magnetic fields, enhance thermal transport, and influence electronic transitions.

  • How can phonon magnetic moments be measured?

    Phonon magnetic moments can be measured using techniques such as spectroscopy and monitoring the shifts in energy levels upon external perturbations.

  • What is the significance of orbital-lattice coupling?

    Orbital-lattice coupling is significant because it can lead to unexpectedly large phonon magnetic moments due to the interaction between lattice vibrations and electronic states.

  • What experimental results were highlighted?

    Recent experiments have shown large phonon magnetic moments in certain materials, which correlate with theoretical predictions.

  • What areas does the research open up for future exploration?

    The research suggests avenues for investigating phonons in new materials, exploring their potential applications in next-generation electronics.

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Legendas
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Rolagem automática:
  • 00:00:00
    so welcome to the come to this uh
  • 00:00:01
    Quantum information and Program start
  • 00:00:03
    quick talk so today we have a swathi
  • 00:00:07
    swathi Chaudhary as our speaker so
  • 00:00:10
    swathi did her BSC from Delhi University
  • 00:00:14
    in 2013.
  • 00:00:17
    her MSC is from IIT kanpur so yeah she
  • 00:00:20
    is wrong
  • 00:00:21
    I'll see if it is that in 2015
  • 00:00:25
    condensy finished at a PhD from Caltech
  • 00:00:29
    in 2021 and she has been a poster joined
  • 00:00:33
    me at the University of Texas Austin at
  • 00:00:35
    Northeastern University in US
  • 00:00:37
    and today's he's talking about
  • 00:00:42
    yes who announced with anger momentum
  • 00:00:44
    magnetic properties and applications
  • 00:00:49
    good afternoon everyone first of all I
  • 00:00:52
    would like to thank you to organizers
  • 00:00:54
    and Island for inviting me for this room
  • 00:00:57
    I'm really grateful for this opportunity
  • 00:00:59
    and it feels really good to be here
  • 00:01:01
    so today I will talk about phone on
  • 00:01:06
    angular momentum about their magnetic
  • 00:01:09
    properties and applications
  • 00:01:12
    so uh first I will uh try to describe
  • 00:01:15
    momentum of phonons then I will talk
  • 00:01:17
    about something called chirophonouns and
  • 00:01:19
    how they respond to different physical
  • 00:01:21
    uh students and then I will talk about
  • 00:01:23
    Magnetic Moment of chiroponomes and the
  • 00:01:26
    mechanism for this form of chirality and
  • 00:01:28
    Magnetic Moment uh then I will present a
  • 00:01:31
    microscopic model for orbital lattice
  • 00:01:33
    coupling like how this Magnetic Moment
  • 00:01:35
    arises from orbital that is covering in
  • 00:01:37
    certain cases then we will talk about
  • 00:01:39
    different materials where this kind of
  • 00:01:41
    latoscopic mechanism can manifest very
  • 00:01:44
    briefly I would also touch on group
  • 00:01:46
    theoretical aspects of Californians
  • 00:01:47
    which would provide us some insight
  • 00:01:49
    about what kind of materials these
  • 00:01:51
    hormones can occur in and then what
  • 00:01:53
    applications
  • 00:01:54
    so to start with what is environmental
  • 00:01:58
    I'm not going to give you a definition
  • 00:01:59
    but
  • 00:02:01
    um you'll know
  • 00:02:03
    um well we have an answer in this book
  • 00:02:05
    so I don't say for me what is angular
  • 00:02:08
    momentum it's the second most important
  • 00:02:10
    topic in this book and it's the most
  • 00:02:12
    difficult topic I think so I think the
  • 00:02:15
    first the most important topic is
  • 00:02:17
    hormone incarcerative
  • 00:02:19
    um
  • 00:02:20
    where we know that um angular momentum
  • 00:02:23
    is very important for lab course and
  • 00:02:25
    nuclei and different kind of
  • 00:02:28
    accompanying between different kind of
  • 00:02:30
    angular momentum is at the heart of very
  • 00:02:32
    exotic phenomenal physics whether it's
  • 00:02:34
    high profile splitting fine splitting or
  • 00:02:37
    magnetism in multiples
  • 00:02:39
    but Magnetic Moment sorry angular
  • 00:02:41
    momentum is also important for photons
  • 00:02:46
    so we know that photons can carry
  • 00:02:48
    something called momentum
  • 00:02:50
    which arises from the circular motion of
  • 00:02:53
    polarization factors so if you look at
  • 00:02:55
    the cross section of this wheel and if
  • 00:02:58
    you have like a circle or equalized beam
  • 00:02:59
    then the polarization Vector moves in a
  • 00:03:01
    closed group and that gives it its
  • 00:03:03
    Preamble momentum depending on whether
  • 00:03:05
    it's rotating in lab circular manner or
  • 00:03:08
    rights of permanent and if you look at
  • 00:03:10
    this perception that at any two points
  • 00:03:12
    if you assume that the pen is correct
  • 00:03:13
    enough then this polarization Vector is
  • 00:03:16
    moving in the face like both of them are
  • 00:03:18
    normally increase on the other hand it
  • 00:03:21
    was realized like about 30 years ago
  • 00:03:23
    that angular momentum can also arise
  • 00:03:25
    from the spatial distribution of this
  • 00:03:27
    so if I take a cross-section of beam and
  • 00:03:30
    I look at two different points on this
  • 00:03:32
    cross section you can have situation
  • 00:03:34
    with cold digestion factor is holding in
  • 00:03:35
    the same direction but there's a phase
  • 00:03:38
    difference and that gives rise to
  • 00:03:40
    orbital angular momentum of photos
  • 00:03:43
    similarly it's proposed that phonons can
  • 00:03:47
    also have angular momentum for example
  • 00:03:49
    you can have circular motion of ions
  • 00:03:51
    which can give rise to something similar
  • 00:03:53
    to spin ambulance
  • 00:03:55
    or you can have a situation where the
  • 00:03:58
    lattice displacement and neighboring
  • 00:04:00
    atoms has some facingness
  • 00:04:02
    it's not exactly similar to OEM beams
  • 00:04:04
    because we have a discrete lattice here
  • 00:04:06
    we have some rotational symmetries which
  • 00:04:08
    kind of restricts the values of L that
  • 00:04:11
    are allowed in this case for example if
  • 00:04:12
    you have like some C and pole symmetry
  • 00:04:14
    like n Fold rotation then you can have
  • 00:04:16
    angular momentum zero one two n minus
  • 00:04:19
    one
  • 00:04:25
    so what is the angular momentum of this
  • 00:04:28
    uh like what is the angular momentum of
  • 00:04:30
    fall on if I take one circular one
  • 00:04:32
    phonon which describes the circular
  • 00:04:35
    polarized lattice vibration like the
  • 00:04:37
    contest form of that circulator is
  • 00:04:39
    vibration what is the format
  • 00:04:42
    let's first consider this classical
  • 00:04:44
    picture here we have this phonon
  • 00:04:47
    displacement which is described by this
  • 00:04:48
    you want to do these are like the atoms
  • 00:04:51
    in your unit cell and I am going to
  • 00:04:54
    focus on your Zone centered hormones
  • 00:04:56
    so we can top only in terms of limit
  • 00:04:58
    cells let's say we have some no recorded
  • 00:05:00
    queue which we can write as Q sine Omega
  • 00:05:02
    T cosine Omega in X in y direction
  • 00:05:05
    so this um
  • 00:05:07
    so this that is vibration would have an
  • 00:05:10
    angular momentum Omega Q Square
  • 00:05:12
    now assuming classical harmonic
  • 00:05:14
    vibration energy for unit cell Omega
  • 00:05:16
    Square Q Square then we can get number
  • 00:05:17
    of phonons and we can show that this
  • 00:05:19
    angular momentum is H quite identical so
  • 00:05:22
    we can say like what panta associated
  • 00:05:24
    with this circular polarized vibration
  • 00:05:26
    has an angular momentum of one Edge
  • 00:05:28
    similarly we can also use this Quantum
  • 00:05:30
    picture where we express these normal
  • 00:05:32
    coordinates in terms of creation and
  • 00:05:34
    Annihilation operators and the same
  • 00:05:36
    thing for velocity and then also uh we
  • 00:05:40
    can write down the circle
  • 00:05:41
    and superposition of X and Y motions and
  • 00:05:45
    then we can show that the samplement
  • 00:05:46
    should be shooting plus minus H bar
  • 00:05:50
    so
  • 00:05:51
    um now I have showed like this should
  • 00:05:53
    carry an argument of plus minus H bar
  • 00:05:56
    um
  • 00:05:57
    so how do I get these forms
  • 00:05:59
    so this Omega comes out of the natural
  • 00:06:03
    material characters
  • 00:06:07
    so it's the the frequency of the phone
  • 00:06:09
    on that we're considering and also like
  • 00:06:11
    I am taking only one standard phonons
  • 00:06:13
    and for now I am focusing on your
  • 00:06:15
    Optical formulas
  • 00:06:19
    so it would be like something in the
  • 00:06:21
    range of like 10 to 100
  • 00:06:25
    so now you can uh get this kind of
  • 00:06:27
    motion by uh getting the superposition
  • 00:06:30
    of like X and Y bonds like vertical
  • 00:06:33
    motion Chronos for example but in most
  • 00:06:35
    cases these two superpositions will have
  • 00:06:38
    the same energy
  • 00:06:39
    but some in in some cases you can get a
  • 00:06:42
    scenario where the two phonons naturally
  • 00:06:44
    polarized and right Circle and polarized
  • 00:06:46
    hormone they get different energy right
  • 00:06:49
    there's a speeding of these phonons
  • 00:06:54
    when the energies associated with rights
  • 00:06:56
    are really polarizing lab circularly
  • 00:06:58
    polarized forms are different so these
  • 00:07:01
    phonons are obtained from like e
  • 00:07:03
    generator
  • 00:07:05
    and then like there can be some internal
  • 00:07:08
    mechanism which can be interested
  • 00:07:12
    um actually this
  • 00:07:17
    is to break in person symmetry or they
  • 00:07:20
    can break at the center of your video
  • 00:07:22
    John if you break families
  • 00:07:25
    recently there has been a lot of
  • 00:07:27
    interest in studying this kind of
  • 00:07:28
    phonons for example these works both of
  • 00:07:31
    these Works have so the first one is the
  • 00:07:33
    theory work where they discuss the
  • 00:07:35
    angular momentum of very very
  • 00:07:36
    correlation so you have a honeycomb
  • 00:07:38
    lattice
  • 00:07:40
    um and you have some very colors so
  • 00:07:42
    these are the hormones which come with
  • 00:07:44
    some finite momentum
  • 00:07:46
    at high 30 points
  • 00:07:51
    that can be different than two and that
  • 00:07:53
    would be different
  • 00:07:55
    literally in this science work it has
  • 00:07:58
    been devastated this kind of hormones
  • 00:08:00
    have been demonstrated experiment where
  • 00:08:02
    they assist some excitations which are
  • 00:08:05
    otherwise stored allowed
  • 00:08:09
    so what makes these hormones interesting
  • 00:08:11
    is how they respond to different current
  • 00:08:13
    quantities
  • 00:08:14
    for example the couple to circulatory
  • 00:08:17
    polarized light in some materials they
  • 00:08:19
    show Circle dipoism they show like
  • 00:08:21
    different absorption for right relaxed
  • 00:08:24
    life in some cases they show you
  • 00:08:28
    [Music]
  • 00:08:35
    for me the most interesting part is
  • 00:08:37
    their magnetic Behavior
  • 00:08:39
    so they coupled with magnetic field and
  • 00:08:42
    this coupling is chirality dependent and
  • 00:08:44
    they can also Exhibit C van impact
  • 00:08:48
    another related process is foreign
  • 00:08:58
    cases they can generate a very large
  • 00:09:01
    effective magnetic field uh in this
  • 00:09:03
    paper it was shown that you can generate
  • 00:09:05
    a magnetic field as large as stupid as
  • 00:09:07
    the uh by exciting such phonons which is
  • 00:09:10
    very high and you can also get like some
  • 00:09:13
    other analogs
  • 00:09:16
    for example
  • 00:09:18
    so today I am going to focus on
  • 00:09:21
    magnetophononic processes I would
  • 00:09:23
    discuss how strong is discovering and
  • 00:09:25
    what is the mechanism behind
  • 00:09:28
    Instagram so first of all why should
  • 00:09:30
    these circularly polarized hormones
  • 00:09:31
    coupled to magnetic field let's consider
  • 00:09:34
    a simple classical scenario so I have
  • 00:09:37
    some ionic solid where we have different
  • 00:09:40
    files with different charges and they
  • 00:09:42
    are moving in circular motion
  • 00:09:44
    so if they are moving in circular motion
  • 00:09:46
    then you would expect them to move like
  • 00:09:48
    they have some angular momentum but they
  • 00:09:50
    will also have some magnetic mode and
  • 00:09:52
    now we can calculate the magnetic
  • 00:09:54
    moments of this full phone on by
  • 00:09:56
    including like different ions and then
  • 00:09:58
    from there we can say that this angular
  • 00:10:01
    momentum would be of the order of
  • 00:10:03
    nuclear magnetism in fact right some
  • 00:10:05
    more disorder but if you choose your
  • 00:10:07
    system carefully you can get some
  • 00:10:10
    Magnetic Moment as high as seven of
  • 00:10:13
    nuclear Magneto and nuclear Magneton is
  • 00:10:16
    like 2000 times smaller than Burma
  • 00:10:19
    so now if we look at phonology matter of
  • 00:10:21
    fact then you would get a very big
  • 00:10:23
    display for example even activated Tesla
  • 00:10:26
    with seven nuclear magnetism
  • 00:10:31
    because 0.002
  • 00:10:35
    so on the basis of the simple classical
  • 00:10:36
    picture we should expect that the phonon
  • 00:10:40
    G Factor would be much smaller
  • 00:10:43
    would be smaller than this movement too
  • 00:10:45
    so
  • 00:10:46
    on the other hand there are some
  • 00:10:48
    experimental books so these are some
  • 00:10:49
    very old experimental goals for 1970s
  • 00:10:52
    and these are on Rare Earth paramagnets
  • 00:10:55
    we have this
  • 00:10:56
    ethereum 3 positive ion which has one
  • 00:10:58
    electron in four effort
  • 00:11:00
    and this material shows this kind of
  • 00:11:03
    split enforce
  • 00:11:04
    enforcements with a Magnetic Moment of
  • 00:11:06
    the order of like seven more
  • 00:11:09
    and similarly there are like a lot of
  • 00:11:11
    materials in this class which show
  • 00:11:14
    similar magnetic moments of the order of
  • 00:11:17
    format
  • 00:11:19
    in fact most recently there has been
  • 00:11:23
    some works on some topological materials
  • 00:11:25
    where similar kind of Magnetic Moment
  • 00:11:29
    has been observed for phonos for example
  • 00:11:31
    in this work on Latin calorie which is
  • 00:11:35
    insulator once you have enough
  • 00:11:37
    doping with the skin then we see that as
  • 00:11:42
    we change
  • 00:11:45
    this is
  • 00:11:47
    and that line shows the condition
  • 00:11:50
    the topological and normal
  • 00:11:52
    so
  • 00:11:54
    in this material like once you go into
  • 00:11:56
    this um topological phase you get some
  • 00:12:00
    phonons which have a Magnetic Moment
  • 00:12:03
    again of the order of government
  • 00:12:05
    and similarly this another material
  • 00:12:07
    which is atroxima material you can see
  • 00:12:09
    this is spreading of left hand and right
  • 00:12:11
    and phones again with the Magnetic
  • 00:12:14
    Moment of core magnet
  • 00:12:15
    so this raises the question where is
  • 00:12:17
    this magnetic model coming from if we
  • 00:12:20
    expect that on the basis of the simple
  • 00:12:21
    classical picture we should get some
  • 00:12:24
    Magnetic Moment of the order of nuclear
  • 00:12:26
    Avenue but what we are seeing
  • 00:12:27
    experimentally it's much higher
  • 00:12:30
    so where is this family moment coming
  • 00:12:33
    well and so the order of Bohr Magneton
  • 00:12:35
    so it kind of indicates that there is
  • 00:12:38
    some contribution from electron still
  • 00:12:41
    somehow electrons are contributing to
  • 00:12:43
    this matter
  • 00:12:45
    and in fact many different mechanisms
  • 00:12:47
    have been identified to account for this
  • 00:12:50
    very large Magnetic Moment performance
  • 00:12:54
    so in first case this Magnetic Moment
  • 00:12:56
    comes from electronically
  • 00:12:58
    which can be explained within the bone
  • 00:13:00
    Oppenheimer approximation so you have a
  • 00:13:02
    phone on you it is you excite some
  • 00:13:05
    lattice vibrations and then your
  • 00:13:07
    laparing system forward adiabatically if
  • 00:13:09
    your electronic bands have some
  • 00:13:10
    non-people topology they accumulate some
  • 00:13:13
    orbital magnetization and that continues
  • 00:13:17
    and for those paramagnets that I would
  • 00:13:19
    I'm showing you in that case it arises
  • 00:13:22
    from coupling with electronic side
  • 00:13:23
    issues which
  • 00:13:26
    and similarly for this drug symmetry it
  • 00:13:29
    arises from the company with Cyclone
  • 00:13:31
    resonances so you have a drug dispersion
  • 00:13:33
    once you apply magnetic field you get
  • 00:13:35
    these Lambda labels and non-honors can
  • 00:13:38
    couple to the excitations with
  • 00:13:41
    the different today I am going to focus
  • 00:13:42
    on this electron insidation mechanism
  • 00:13:45
    it's a non-edible
  • 00:13:47
    open Hardware approximation
  • 00:13:53
    so this mechanism operates in these rare
  • 00:13:55
    paramagnets where phones support to
  • 00:13:58
    crystalline
  • 00:13:59
    foreign
  • 00:14:01
    we asked whether this mechanism can also
  • 00:14:03
    occur in some other materials
  • 00:14:06
    for example can it occur in some new
  • 00:14:07
    orbital magnets and can it occur in some
  • 00:14:10
    other magnets where you have like some
  • 00:14:12
    kind of super extreme interactions
  • 00:14:15
    and is it possible to estimate this
  • 00:14:18
    estimate value of this orbital lattice
  • 00:14:20
    coupling estimate the value of this
  • 00:14:22
    phonon magnetic movement from a
  • 00:14:24
    microscope
  • 00:14:25
    so those Works had provided a model but
  • 00:14:27
    they did not provide a microscope model
  • 00:14:29
    to estimate those
  • 00:14:32
    bags so so first I will describe the
  • 00:14:35
    model which accounts for this phonon
  • 00:14:37
    Magnetic Moment arising from orbital
  • 00:14:39
    lattice coupling so it's a
  • 00:14:41
    generalization
  • 00:14:42
    of
  • 00:14:44
    what so it's a generalization of this
  • 00:14:46
    work where this work provided a theory
  • 00:14:49
    for this 4f rear back means but they did
  • 00:14:52
    not provide a microscopic model
  • 00:14:57
    so this is so here are like some minimal
  • 00:14:59
    ingredients of this model so we have a
  • 00:15:01
    ground state which is W regenerate and
  • 00:15:03
    these two states are Thai University
  • 00:15:04
    Partners so we have agreement upgrade
  • 00:15:06
    and these states are they have some
  • 00:15:08
    fixed Android momentum J Alpha and
  • 00:15:11
    magnetic and J minus
  • 00:15:14
    and then we have some
  • 00:15:16
    of other states at a slightly higher
  • 00:15:19
    energy which we call side three side
  • 00:15:21
    four they are also clever doublets but
  • 00:15:23
    but with very different aluminum
  • 00:15:25
    population
  • 00:15:27
    yeah if you have to go from State one to
  • 00:15:28
    state three that would include some
  • 00:15:30
    angular momentum Exchange
  • 00:15:33
    and now you can have phone also these
  • 00:15:35
    are the two phones that I have shown for
  • 00:15:38
    um it's either like the two components
  • 00:15:41
    of a w degenerate phonon mods you can
  • 00:15:43
    think of them as X motion and by motion
  • 00:15:45
    for example
  • 00:15:46
    so now
  • 00:15:48
    we have this electrophone interaction
  • 00:15:51
    where these hormones couple these
  • 00:15:53
    different states basically what these
  • 00:15:55
    phones are doing these phonons are
  • 00:15:56
    compension side three side to side four
  • 00:15:58
    in this complicated matter and this the
  • 00:16:00
    form of this interaction is written by
  • 00:16:03
    timing Association
  • 00:16:06
    so these interactions can be explained
  • 00:16:08
    can be represented by these vertices and
  • 00:16:13
    then we can calculate like what they do
  • 00:16:15
    the phonon energies while using
  • 00:16:19
    case where this is the greens function
  • 00:16:22
    Matrix for two modes so we have two
  • 00:16:24
    modes that's right we have two
  • 00:16:26
    components and if you have to like find
  • 00:16:28
    a frequency of these phones you can just
  • 00:16:29
    look at the denominator pretty procure
  • 00:16:31
    that's a very simplistic thing
  • 00:16:34
    now we include the first Corrections
  • 00:16:36
    from the these interaction vertices and
  • 00:16:40
    that modifies the great function Matrix
  • 00:16:43
    and it introduces the cell energy terms
  • 00:16:45
    so we have this um of diagonal term
  • 00:16:48
    which is uh most important for us so
  • 00:16:51
    this soft algorithm basically it splits
  • 00:16:53
    up the two phonons so you can think of
  • 00:16:55
    this together two by two Matrix where it
  • 00:16:57
    was silently earlier now you have the
  • 00:16:59
    assumpty maxing of
  • 00:17:01
    and also I will show later that these
  • 00:17:05
    coupling constants have this problem
  • 00:17:08
    now once we uh get these phonons these
  • 00:17:11
    functions then we can get one on
  • 00:17:13
    energies by solving this equation which
  • 00:17:15
    can be done analytically and then to the
  • 00:17:18
    first order in magnetic field begins so
  • 00:17:22
    this magnetic field enters into picture
  • 00:17:23
    because this row is non-zero if you have
  • 00:17:27
    Delta one
  • 00:17:37
    or if the population of the two levels
  • 00:17:40
    in the ground state planning for this
  • 00:17:41
    different you can think of damage up and
  • 00:17:43
    down so by applying magnetic field you
  • 00:17:46
    can change the
  • 00:17:49
    in order to get these terms non-zero
  • 00:17:51
    will have to Great Value
  • 00:17:55
    so this we say that it has two
  • 00:17:56
    contributions one arises from the
  • 00:17:59
    differences into
  • 00:18:01
    um
  • 00:18:01
    cases and another arises from the
  • 00:18:04
    population difference of two states
  • 00:18:06
    within the lower energy uh manifold and
  • 00:18:09
    this storm is directly proportional
  • 00:18:12
    for a paramagnet it will have like a 10
  • 00:18:14
    hyperbolic term it will also have a
  • 00:18:16
    temperature dependence
  • 00:18:18
    if you want to consider a simple picture
  • 00:18:20
    sorry
  • 00:18:22
    so you can also think like if you have
  • 00:18:24
    the stigma y kind of term the new phonon
  • 00:18:26
    modes also get modified earlier you had
  • 00:18:28
    X and Y which were your eigenous States
  • 00:18:30
    and the system was degenerate right once
  • 00:18:32
    you include those interactions you get
  • 00:18:35
    these new phonon mods and they are this
  • 00:18:37
    kind of superposition which
  • 00:18:39
    are priority
  • 00:18:43
    now if we want to consider we can
  • 00:18:44
    actually visualize this whole
  • 00:18:46
    interaction in a very simple way let's
  • 00:18:48
    say um if this condition is satisfied
  • 00:18:50
    then you can write it down in terms of
  • 00:18:52
    this lab cell really polarized phonon
  • 00:18:54
    displacement and that's certainly for
  • 00:18:56
    them all right
  • 00:18:58
    so what I have I have this excitation
  • 00:19:01
    electronic excitation on the magnetic
  • 00:19:04
    ion which involves a magnetic which
  • 00:19:06
    involves a change of angular momentum by
  • 00:19:08
    one let's say and then we have a phonon
  • 00:19:10
    which also carries an angular moment
  • 00:19:12
    so now you can these two uh excitations
  • 00:19:15
    will be hybridized it's very very
  • 00:19:16
    similar to what you see for exit one
  • 00:19:18
    polarity
  • 00:19:20
    coupling x01 coupling and you get those
  • 00:19:23
    four atoms so so this follow-on uh this
  • 00:19:27
    stats are very polarized phone on
  • 00:19:28
    couples to this excitation and the
  • 00:19:30
    opposite phonon which is time remember
  • 00:19:31
    so copy of this phone on it couples with
  • 00:19:34
    another excitation which is the time it
  • 00:19:36
    was a copy of that explanation both of
  • 00:19:38
    them hybridize and that changes the
  • 00:19:40
    frequencies of these formats well it
  • 00:19:42
    changes the frequencies but they still
  • 00:19:44
    remain the same if tan reverse is
  • 00:19:45
    symmetry is
  • 00:19:48
    you can also visualize this process like
  • 00:19:50
    this where I have two halogenables for
  • 00:19:51
    phonons and two energy levels citations
  • 00:19:54
    and they hybridize it as you can see now
  • 00:19:57
    we have two phones whose energies are
  • 00:19:59
    different but they are still teacher
  • 00:20:00
    rate but once you apply magnetic field
  • 00:20:02
    then the speed Generac is lifted for two
  • 00:20:05
    reasons one that excitations that I
  • 00:20:09
    showed you this Delta one entitled to
  • 00:20:11
    their energies become different second
  • 00:20:13
    the population for excitation one and
  • 00:20:15
    excitation two they also equal to
  • 00:20:18
    so as a result of this this decent ratio
  • 00:20:22
    of two phonons is lifted and it's lifted
  • 00:20:24
    in a way that the new item votes are
  • 00:20:26
    right circular polarized and last
  • 00:20:27
    circular importance
  • 00:20:29
    and this uh displaying is non-zero only
  • 00:20:33
    if the level minus WC over F minus F2 is
  • 00:20:36
    0 which I mentioned now this is
  • 00:20:39
    spreading depends on a lot of factors
  • 00:20:40
    first thing which we need for this is
  • 00:20:42
    pretty is that these Deltas need to be
  • 00:20:45
    closer in energy to phonons and that's a
  • 00:20:49
    very um
  • 00:20:50
    difficult thing to do like that that's
  • 00:20:52
    very material specific thing because
  • 00:20:54
    photos depend on material like their
  • 00:20:57
    fragment system and materials and
  • 00:20:58
    similarities
  • 00:20:59
    electronic excitations
  • 00:21:04
    and another thing that we need is the
  • 00:21:06
    electronic G factor of States because
  • 00:21:08
    how much they would be shifted how much
  • 00:21:10
    their populations would change with
  • 00:21:11
    applied magnetic field would depend on
  • 00:21:13
    this camera
  • 00:21:15
    and of course language that would decide
  • 00:21:17
    the population in that
  • 00:21:21
    so another uh there's one more Factor so
  • 00:21:25
    all of these things we can measure but
  • 00:21:27
    there's one more factor that is
  • 00:21:28
    excitations
  • 00:21:33
    so here I'm I'm considering an orbital
  • 00:21:37
    lattice coupling mechanism so what is
  • 00:21:39
    happening like you have a magnetic
  • 00:21:40
    material you have a magnetic ion which
  • 00:21:43
    is surrounded by some ligands so for
  • 00:21:45
    example some oxygen ions or chlorine
  • 00:21:47
    ions IELTS and once you excite a phonon
  • 00:21:50
    which reduces the symmetry of the system
  • 00:21:53
    it changes the crystallographic field
  • 00:21:55
    around that magnetic
  • 00:21:57
    data and that change that introduces
  • 00:21:59
    some perturbation to that
  • 00:22:00
    crystallographic field and now you can
  • 00:22:02
    expand the crystalline to feel in terms
  • 00:22:04
    of these states of that magnetic ion and
  • 00:22:07
    then you can find these coupling forces
  • 00:22:10
    and this is the app which we use because
  • 00:22:13
    like these states that I talked about I
  • 00:22:15
    said I never characterized by some J and
  • 00:22:17
    MJ and this energy is coming from
  • 00:22:19
    orbital and this will take your freedom
  • 00:22:21
    now if you change if you point out this
  • 00:22:22
    crystall active field around this ion
  • 00:22:24
    that can compute
  • 00:22:28
    first we apply this to this well
  • 00:22:30
    established today so prayer or
  • 00:22:32
    trihilites which was studied in 1970s
  • 00:22:35
    so um this is
  • 00:22:37
    cereal trichloride where we have this
  • 00:22:40
    serial three positive wine which is
  • 00:22:42
    surrounded by nine taurine ions and this
  • 00:22:46
    is a Four f orbital system
  • 00:22:49
    coupling is very strong
  • 00:22:52
    so if I take like one electron in Forum
  • 00:22:54
    system
  • 00:22:55
    if
  • 00:22:56
    then you have all of your F4 bedrooms
  • 00:22:59
    have the same energy but once you have
  • 00:23:00
    some economic coupling which is very
  • 00:23:02
    strong for these materials as you keep
  • 00:23:04
    on moving down a periodic table this
  • 00:23:06
    will all the company keeps on increasing
  • 00:23:08
    so this country has it's going to copy
  • 00:23:10
    of the odor finder down
  • 00:23:12
    and F electrons are very well shaded so
  • 00:23:14
    they don't feel the crystal lactic
  • 00:23:16
    fields of bacterial effects that much
  • 00:23:18
    for this to feel uh some effect from
  • 00:23:21
    Crystal activities in this case you get
  • 00:23:23
    these um this distribution once you
  • 00:23:26
    apply once you can see the effects of
  • 00:23:28
    crystallactive field as perturbation
  • 00:23:30
    so the point to note at here is that you
  • 00:23:33
    have these electric labels for these low
  • 00:23:36
    energy low energy levels of this
  • 00:23:38
    material which are characterized by J Pi
  • 00:23:40
    by 2 and mg with different values so
  • 00:23:42
    they are all coming from the same
  • 00:23:48
    engine and next we consider some each
  • 00:23:51
    phonons so we can obtain the
  • 00:23:53
    displacement for for these columns from
  • 00:23:55
    group Theory
  • 00:23:56
    and then we uh find out like how they
  • 00:23:59
    change this Crystal
  • 00:24:02
    and then you write down in terms of
  • 00:24:04
    the X and Y equals
  • 00:24:06
    so in terms of like position or
  • 00:24:08
    coordinates around that same
  • 00:24:10
    um
  • 00:24:11
    and what it does it basically introduces
  • 00:24:14
    coupling between these different
  • 00:24:16
    Industries for example when you write
  • 00:24:17
    this from cycling don't so these states
  • 00:24:21
    for J and M J you can see that they are
  • 00:24:24
    coupling like different
  • 00:24:26
    different um States
  • 00:24:30
    so in this case this vertical formula is
  • 00:24:32
    coupling plus minus five by two by plus
  • 00:24:34
    minus 3 by 2 which is about 40 mud and
  • 00:24:38
    this formula has energy 23rd scales are
  • 00:24:41
    battery which is good enough
  • 00:24:43
    usually that doesn't happen because like
  • 00:24:45
    this exercise
  • 00:24:50
    and then we apply this model and study
  • 00:24:53
    like all this is feeding off these
  • 00:24:55
    phonons changes with magnetic field and
  • 00:24:57
    this is what we get we basically see a
  • 00:24:59
    splitting of about men you see the
  • 00:25:01
    saturation is splitting of about 1.2 mm
  • 00:25:04
    and the saturation is coming from this
  • 00:25:06
    10 hyperbolic Factor because we had this
  • 00:25:08
    low energy manifolded up and down here
  • 00:25:12
    and you can see that it Compares quite
  • 00:25:15
    well with these results from
  • 00:25:17
    1970s their their uh saturation
  • 00:25:20
    spreading was 18 scientific reverse and
  • 00:25:22
    it was the saturated
  • 00:25:24
    as well
  • 00:25:26
    we should be looking at the cell 200
  • 00:25:29
    this phone one at 200 centimeters
  • 00:25:37
    in this case which is characterized by
  • 00:25:40
    this kind of motion where these
  • 00:25:43
    um chlorine ions are moving out of X by
  • 00:25:46
    K like they are moving along c Direction
  • 00:25:47
    but there is a relative phase a
  • 00:25:50
    different
  • 00:25:51
    items similarly we can now apply this
  • 00:25:54
    model to other phonons and we see that
  • 00:25:57
    there is another phone on E to G which
  • 00:25:59
    couples these plus minus five by two and
  • 00:26:02
    plus minus one by two and
  • 00:26:04
    six other formula and in this case the
  • 00:26:06
    combination like this color
  • 00:26:07
    superposition gives rise to the circular
  • 00:26:08
    motion
  • 00:26:10
    so what we see is that there is a
  • 00:26:12
    consider
  • 00:26:16
    ation which indicates that these phonons
  • 00:26:18
    can carry a Magnetic Moment of the order
  • 00:26:19
    of four magnet known in this case at 10
  • 00:26:22
    Kelvin this first phonon shows uh
  • 00:26:24
    Magnetic Moment of three more Magneto
  • 00:26:28
    which at least by order of magnitude
  • 00:26:30
    Wise It's very uh you know it's a good
  • 00:26:33
    argument with the experimental disease I
  • 00:26:36
    mean this is a very crude model so I
  • 00:26:38
    think we can't expect a very very good
  • 00:26:40
    argument but I think it's good enough
  • 00:26:42
    now next question we asked like have we
  • 00:26:45
    tested this model for the their
  • 00:26:46
    paramagnets can we apply this kind of
  • 00:26:49
    process into
  • 00:26:53
    it so let's first very briefly review
  • 00:26:55
    what is different
  • 00:26:58
    system that I was showing you it had
  • 00:27:01
    like a very strong economic coupling and
  • 00:27:03
    eventually Queen excitation was
  • 00:27:04
    splitting of these fingers
  • 00:27:07
    on the other hand for day lactose
  • 00:27:09
    systems you know that crystalline
  • 00:27:10
    excitations are very crystallographic
  • 00:27:12
    field energies are very high so we see
  • 00:27:14
    this is splitting of the orbitals in t2g
  • 00:27:16
    EG which is on plot of one so this is
  • 00:27:20
    not compatible with Optical phonons
  • 00:27:22
    because they are virtually lower than
  • 00:27:25
    however there are mechanisms too which
  • 00:27:27
    these t2g can spring for them for
  • 00:27:30
    example
  • 00:27:31
    or some other events
  • 00:27:32
    for example you can have some tribal
  • 00:27:34
    Distortion in your system that can also
  • 00:27:37
    split up these labels further
  • 00:27:42
    in fact recently uh
  • 00:27:45
    in fact recently
  • 00:27:47
    there's a group at Beauty Austin
  • 00:27:49
    professor in English who have detected a
  • 00:27:51
    very high Magnetic Moment
  • 00:27:55
    on point 11 cobal type weight so in this
  • 00:27:58
    case Cobalt three positives
  • 00:28:01
    forward too positive it has
  • 00:28:04
    seven kilometers in its outermost shell
  • 00:28:06
    and they have noticed the form of
  • 00:28:09
    Magnetic Moment of the order of four
  • 00:28:10
    magnetone again and to the best of her
  • 00:28:12
    knowledge this is the first such example
  • 00:28:14
    community
  • 00:28:17
    so now we uh
  • 00:28:19
    apply a wall to this setting but before
  • 00:28:22
    that I would very quickly talk about
  • 00:28:24
    like how animation is
  • 00:28:26
    so this Magnetic Moment is measured by
  • 00:28:29
    uh to this healthy Resort Planet romance
  • 00:28:32
    spectroscopy so you have this course
  • 00:28:34
    circular Channel where you sat in the
  • 00:28:36
    right Circle that's hormone
  • 00:28:39
    polarized phonon and then what they
  • 00:28:41
    notice is that this Peak for this phone
  • 00:28:44
    when it spins up as you apply magnetic
  • 00:28:48
    [Music]
  • 00:28:52
    I will talk about that too like why this
  • 00:28:55
    one direction is important
  • 00:28:57
    and then it indicates that this exchange
  • 00:29:00
    of environment which is happening it's
  • 00:29:01
    basically going to this excitation this
  • 00:29:04
    phone on excitation
  • 00:29:06
    so here again the uh so we are proposing
  • 00:29:09
    that in this case this mechanism is
  • 00:29:11
    arising from this orbital status
  • 00:29:13
    so in order to understand that let's
  • 00:29:15
    first look at what is the structure of
  • 00:29:18
    this material
  • 00:29:20
    s
  • 00:29:21
    many positive ion since uh if it's okay
  • 00:29:24
    to engage of oxygen ions which is
  • 00:29:26
    slightly dysphorically struggling
  • 00:29:28
    distorted which means that the Symmetry
  • 00:29:30
    side symmetry is reduced to threefold
  • 00:29:33
    rotation
  • 00:29:34
    and there is a considerable coupling so
  • 00:29:38
    um we cannot like read any of them as
  • 00:29:40
    for Innovations but what we see like
  • 00:29:43
    once we take into account this uh spin
  • 00:29:45
    or the coupling and criminal Distortion
  • 00:29:46
    and this kind of things have been used
  • 00:29:48
    like this electronic energy diagram as
  • 00:29:51
    each one it is
  • 00:29:53
    so um we are going to focus on these two
  • 00:29:56
    low identity states which can get Rise
  • 00:29:59
    by mg plus minus one by two
  • 00:30:02
    oh
  • 00:30:03
    I mean technically they cannot be
  • 00:30:05
    characterized by fixed J but
  • 00:30:06
    predominantly this lower manifold is and
  • 00:30:09
    the upper one is
  • 00:30:15
    so now what happens uh now we have
  • 00:30:18
    easily phonons here which have energies
  • 00:30:21
    around 20 and maybe so 26 are maybe 23
  • 00:30:24
    are maybe this excitation has energy
  • 00:30:26
    going to take everything which is again
  • 00:30:28
    putting it in close proximity uh like
  • 00:30:31
    these two energies are to close
  • 00:30:32
    proximity so it's highly visible that
  • 00:30:34
    this kind of effect might happen
  • 00:30:37
    but this material is very different than
  • 00:30:39
    what I was talking about earlier because
  • 00:30:42
    that was a 4X system I had only one
  • 00:30:44
    electron and it was a parabang rate
  • 00:30:49
    however in this material there are two
  • 00:30:52
    differences first is that these two
  • 00:30:54
    states these two energy manifolds that
  • 00:30:56
    are important for my model they are
  • 00:30:58
    coming from different J values
  • 00:31:00
    the second there is soft magnetic phase
  • 00:31:02
    transmission so once you fall below 38
  • 00:31:04
    Kelvin what happens is you get this
  • 00:31:06
    antiviromagnetic
  • 00:31:08
    it is
  • 00:31:16
    foreign
  • 00:31:18
    which means that from exchange
  • 00:31:20
    interactions you will get some magnetic
  • 00:31:23
    field even if you are not applying any
  • 00:31:24
    external magnetic field you will get
  • 00:31:25
    some in-plane magnetism
  • 00:31:29
    so it hybridizes I'm sorry so it opens
  • 00:31:32
    up a gap in these two states that I I
  • 00:31:34
    will show you earlier in these two
  • 00:31:36
    states and it hybridizes it them in a
  • 00:31:39
    way that the angular momentum alone Z
  • 00:31:41
    Direction comes out
  • 00:31:42
    the phonon carries angular moment
  • 00:31:46
    s but once you start applying back when
  • 00:31:48
    you feel you can change the eigenous
  • 00:31:50
    state so these states such that they
  • 00:31:53
    gain some annual fundam which makes this
  • 00:31:55
    process which makes this mechanism
  • 00:31:57
    physical
  • 00:31:59
    however the temperature dependence would
  • 00:32:01
    be very different earlier we had that 10
  • 00:32:04
    hyperbolic kind of dependence but here
  • 00:32:07
    um it would be very different depending
  • 00:32:09
    on the magnetic system
  • 00:32:12
    so first we calculate the splitting for
  • 00:32:14
    T greater than t n which is the
  • 00:32:16
    paramagnetic case and here again we
  • 00:32:19
    find we apply the same microscopic model
  • 00:32:22
    and then we find that magnetic movement
  • 00:32:24
    is
  • 00:32:25
    0.1 and 0.
  • 00:32:28
    but next we stay temperature friends and
  • 00:32:31
    for temperature Trends I am going to
  • 00:32:32
    focus on living one of those four
  • 00:32:34
    numbers that is 33 I mean
  • 00:32:36
    um
  • 00:32:38
    so then we include this in plane
  • 00:32:40
    magnetic field and we take into account
  • 00:32:42
    the identities like how these eigen
  • 00:32:44
    states are changing with this applied
  • 00:32:45
    magnetic field and this applied magnetic
  • 00:32:47
    field is itself a function of
  • 00:32:49
    temperature because it depends on
  • 00:32:50
    magnetic ordering as you keep on going
  • 00:32:52
    below a new temperature keeps on
  • 00:32:54
    increasing so you can already see that
  • 00:32:56
    there is some saturation in this formula
  • 00:32:59
    moment which is indicative of this in
  • 00:33:01
    plane external magnetic field
  • 00:33:04
    and these are experiment these are the
  • 00:33:07
    values measured from experiment so um
  • 00:33:10
    our Theory matches well for order of
  • 00:33:13
    magnitude like we say 0.15 uh for family
  • 00:33:16
    node and the trend is very similar
  • 00:33:18
    however it doesn't accumulative well
  • 00:33:20
    comparatively it could be because like
  • 00:33:23
    our model is to approve this microscopic
  • 00:33:25
    model for lack of component coupling is
  • 00:33:27
    not giving us the right order to
  • 00:33:30
    by changing this
  • 00:33:33
    orbitalized swiveling and we formed a
  • 00:33:35
    reasonably good fit if we use some value
  • 00:33:36
    which is twice then that we obtained
  • 00:33:38
    from our microscopic model
  • 00:33:41
    so um so this orbital access coupling
  • 00:33:43
    model can also be applied to some Data
  • 00:33:46
    Systems that's one of our main countries
  • 00:33:50
    now very briefly you might ask like
  • 00:33:52
    where else should I look for this kind
  • 00:33:54
    of phonons I think good care can provide
  • 00:33:57
    us some insight so what was common in
  • 00:33:59
    these
  • 00:34:00
    two different materials was like we had
  • 00:34:02
    some WD General phonons
  • 00:34:04
    it surely presented by these irreducible
  • 00:34:06
    representations EGU and then your time
  • 00:34:09
    was a breaking um
  • 00:34:12
    yeah then once you break time it was
  • 00:34:14
    intimidate these um irreducible
  • 00:34:16
    representations should break into two
  • 00:34:18
    one Dimensions uh you don't have to go
  • 00:34:21
    through the details of all those terms
  • 00:34:22
    but you can think of this thing like
  • 00:34:24
    that so you have let's say p x and P Y
  • 00:34:26
    orbitals Let's ignore PC for one moment
  • 00:34:28
    and you apply some magnetic field your
  • 00:34:30
    break time is symmetry so your new eigen
  • 00:34:33
    States become P X Plus y b y and p x
  • 00:34:35
    minus i t y so the same thing can be
  • 00:34:38
    reflected in these irreducible
  • 00:34:40
    representations which you can read from
  • 00:34:42
    character tables
  • 00:34:45
    and now the possibilities of your system
  • 00:34:47
    should be such that they should allow an
  • 00:34:48
    exit back because the angular momentum
  • 00:34:50
    that we are looking at is
  • 00:34:53
    so if you look at the character tables
  • 00:34:55
    then an axial Vector like the Z
  • 00:34:58
    component of this axis Vector should
  • 00:35:00
    occur in this previous which means that
  • 00:35:03
    it should not be affected by any
  • 00:35:05
    component of your symmetry right if you
  • 00:35:07
    do any of those symmetry operations you
  • 00:35:09
    should be Studio at the same exercise
  • 00:35:11
    for example that is the case for C3 and
  • 00:35:14
    for c3h where you have in
  • 00:35:17
    where your mirror plane is perpendicular
  • 00:35:19
    rotation access
  • 00:35:22
    um
  • 00:35:22
    I think I'm a good thing to do so it
  • 00:35:24
    reactants your um
  • 00:35:27
    mirror play you're you're basically your
  • 00:35:29
    rotation exercising your rear plane so
  • 00:35:31
    it doesn't change the accelerator to
  • 00:35:34
    change the ID batteries that's
  • 00:35:36
    perpendicular to the potential access
  • 00:35:38
    and on the basis of this kind of
  • 00:35:40
    symmetry analysis uh we made this list
  • 00:35:43
    of magnetic Point groups so this
  • 00:35:45
    information about error display
  • 00:35:47
    representations can be obtained from
  • 00:35:52
    server and we found these magnetic Point
  • 00:35:55
    groups which can allow for this kind of
  • 00:35:58
    drone centered kind of forms and in fact
  • 00:36:00
    this example of cobalt diet made that as
  • 00:36:02
    its discussing it was in this case
  • 00:36:04
    for example you can also have a
  • 00:36:06
    situation like this yesterday you have
  • 00:36:07
    some C3 symmetry which allows this kind
  • 00:36:10
    of axle vector then you also have let's
  • 00:36:13
    say some twofold rotation which Maps it
  • 00:36:15
    to negative open cells so you cannot get
  • 00:36:17
    n you cannot get an ample momentum in
  • 00:36:20
    this case so you cannot get a car
  • 00:36:22
    formula in this case however if you have
  • 00:36:24
    a set of beer C2 is broken but C2 times
  • 00:36:27
    time which is preserved and he can have
  • 00:36:29
    the same signal the sexual opposite
  • 00:36:32
    that's for example the case for this um
  • 00:36:35
    magnetic Point group
  • 00:36:37
    now uh what are some other situations
  • 00:36:40
    where this kind of orbital lattice
  • 00:36:42
    coupling mechanism can arise
  • 00:36:46
    so for example I think this mechanism
  • 00:36:48
    can also arrive in 40 magnets and
  • 00:36:51
    lithium trichloride might be a good
  • 00:36:53
    candidate it has reasonable spin orbit
  • 00:36:55
    coupling so it's been orbit coupling is
  • 00:36:56
    usually higher for 4D and 5A in
  • 00:36:59
    comparison between
  • 00:37:03
    and it has some low energy excitations
  • 00:37:06
    which are at about 100 mbv and some
  • 00:37:08
    Optical Corners which are responsive
  • 00:37:09
    yeah I mean the scales are not matching
  • 00:37:11
    very well so the fact would we support
  • 00:37:13
    the curve but I think it should
  • 00:37:15
    be stronger than incredible so we
  • 00:37:17
    haven't done that calculate
  • 00:37:19
    and another question we can ask like
  • 00:37:20
    right now is breaking tablets in
  • 00:37:22
    Symmetry by applying magnetic field but
  • 00:37:24
    what about if you have a ferromagnet if
  • 00:37:25
    your magnetic order is such that you get
  • 00:37:27
    some magnetic fields reduction
  • 00:37:30
    symmetry in a manner
  • 00:37:43
    um I don't know any such examples at
  • 00:37:44
    this point but there's this paper for
  • 00:37:46
    World chromium iodide where they have
  • 00:37:48
    this kind of ferromagnetic setup uh but
  • 00:37:50
    they explain this Magnetic Moment from
  • 00:37:53
    the basis of coupling with that loss
  • 00:37:55
    another scenario you can imagine is
  • 00:37:58
    fluke engineering
  • 00:37:59
    so you apply a circularly polarized
  • 00:38:01
    light that breaks familiarity of your
  • 00:38:04
    system and that uh gives you chiral
  • 00:38:07
    forms for example that can occur in
  • 00:38:09
    graphene so circularly polarized driven
  • 00:38:11
    graphene circular polarized like ribbon
  • 00:38:13
    graphene is very well studied both
  • 00:38:14
    theoretically and experimentally and
  • 00:38:16
    it's known that
  • 00:38:23
    so we can ask like what would happen
  • 00:38:25
    like if you couple phonons to these
  • 00:38:27
    stroke events these new bands which have
  • 00:38:29
    some finite qualification and this is
  • 00:38:31
    One Direction which I am pursuing with
  • 00:38:33
    Professor Takashi Oka from University of
  • 00:38:35
    Tokyo and my postdoc advisor Grandfield
  • 00:38:41
    so having talked about all these
  • 00:38:42
    mechanisms now let me very briefly talk
  • 00:38:46
    about applications
  • 00:38:47
    so we have these current hormones where
  • 00:38:50
    we have this kind of circular vibrations
  • 00:38:52
    now what to do with that
  • 00:38:54
    they also respond very strongly to
  • 00:38:55
    magnetic field
  • 00:38:58
    so first thing that we can do with them
  • 00:39:01
    so I think I put that reference earlier
  • 00:39:03
    is that they can generate a very large
  • 00:39:05
    effective magnetic field uh I think the
  • 00:39:08
    microscopic model that I applied for for
  • 00:39:11
    Magnetic Moment would also explain this
  • 00:39:13
    giant effective magnetic field in those
  • 00:39:15
    papers it was described on a very
  • 00:39:16
    phenomenological basis like uh they had
  • 00:39:18
    used a very different analysis so one
  • 00:39:21
    thing like if you can generate this kind
  • 00:39:22
    of giant effective magnetic field by
  • 00:39:25
    applying an external laser it means that
  • 00:39:27
    you can basically control the
  • 00:39:29
    magnetization on an ultra Fast Times
  • 00:39:31
    case which is very important for its
  • 00:39:33
    Electronics so you can control the
  • 00:39:34
    magnetization of your system at Ultra
  • 00:39:36
    first time skills and that can have some
  • 00:39:38
    major implications for information
  • 00:39:40
    processing
  • 00:39:41
    and as I mentioned earlier in that paper
  • 00:39:43
    it was shown that you can achieve very
  • 00:39:45
    high magnetic fields which can help you
  • 00:39:47
    to study phase transitions at very high
  • 00:39:49
    magnetic field in some materials and
  • 00:39:52
    then you can also use that effective
  • 00:39:53
    magnetic field to control the magnitude
  • 00:39:59
    similarly another aspect of these chiral
  • 00:40:01
    phonons is
  • 00:40:03
    um
  • 00:40:03
    in some cases they are also connected to
  • 00:40:07
    non-trivial phonon band topology that is
  • 00:40:10
    one thing and they can also exhibit this
  • 00:40:13
    thermal Roll Effect
  • 00:40:15
    um I think there are two contributions
  • 00:40:17
    in this case one comes from the
  • 00:40:19
    non-trivial topology of these phonos and
  • 00:40:22
    one from these chiral properties based
  • 00:40:25
    on phonon algorithm momentum so now you
  • 00:40:27
    can have much more efficient thermal
  • 00:40:29
    transport with these chiropodons and
  • 00:40:32
    this kind of chiral phonon based thermal
  • 00:40:35
    transport has been shown in cup rates in
  • 00:40:37
    this paper
  • 00:40:38
    um
  • 00:40:41
    another implication that you can have is
  • 00:40:43
    into the optoelectronics
  • 00:40:45
    so you can have cardio phone assisted
  • 00:40:47
    transition there are certain transitions
  • 00:40:49
    in some materials which are forbidden
  • 00:40:52
    due to angular momentum conservation
  • 00:40:54
    like you have like much higher angular
  • 00:40:56
    momentum you need much higher angular
  • 00:40:57
    momentum for those transitions but if
  • 00:41:00
    you can like have some chiral phone on
  • 00:41:02
    assistive transition where some angular
  • 00:41:04
    momentum is provided by the carophonal
  • 00:41:06
    then those transitions can be allowed or
  • 00:41:09
    it can have some important implications
  • 00:41:10
    for exit on phonon coupling as well
  • 00:41:13
    so I discussed like the energy is like
  • 00:41:16
    how this phonons even effect manifests
  • 00:41:17
    but there is also another aspect of
  • 00:41:19
    these guidelines that is this Capital
  • 00:41:22
    processes so how do they scatter because
  • 00:41:24
    they carry angular momentum so their
  • 00:41:26
    scattering would be much more restricted
  • 00:41:28
    which makes them very long-lived and it
  • 00:41:31
    can have some very interesting
  • 00:41:33
    consequences for spin relaxation and
  • 00:41:36
    scattering uh another thing that this
  • 00:41:40
    model can do in our case like if we
  • 00:41:43
    apply this model and we study some kind
  • 00:41:44
    of phonons and there's splitting in
  • 00:41:46
    magnetic field that can also serve as a
  • 00:41:48
    pro for orbital lattice coupling or in
  • 00:41:51
    some cases a pro for electronic band
  • 00:41:53
    temperature
  • 00:41:54
    with this I would like to conclude I
  • 00:41:57
    think I still have time but
  • 00:42:00
    um so I provided a microscopic model for
  • 00:42:03
    phonon magnetic movement which was based
  • 00:42:05
    on orbital lattice coupling and then we
  • 00:42:08
    provided some estimates of magnetic
  • 00:42:10
    movements in different classes of
  • 00:42:11
    materials and we also
  • 00:42:13
    predict some new materials where this
  • 00:42:16
    kind of effects can occur and some new
  • 00:42:17
    mechanisms for example this flowkey
  • 00:42:19
    engineered thing
  • 00:42:21
    however there are a lot of aspects of
  • 00:42:23
    these car reformers which haven't been
  • 00:42:25
    installed it yet because this area is
  • 00:42:26
    very new for example the model that had
  • 00:42:30
    considered was a molecular model so I
  • 00:42:31
    just looked at the unit cell and I
  • 00:42:33
    treated that whole system as a molecule
  • 00:42:35
    but now you can also have like ignorant
  • 00:42:38
    bands like you have these uh bands in
  • 00:42:40
    your system and you might ask like how
  • 00:42:42
    do electrons couple do those magnetic
  • 00:42:45
    eyes which are those magnetic degrees of
  • 00:42:47
    freedom which are moved around
  • 00:42:49
    uh similarly they can also couple to
  • 00:42:51
    some other excitations in the system
  • 00:42:52
    like magnets and I've looked I looked at
  • 00:42:56
    only at this whole centered phonons but
  • 00:43:00
    what about finite K followers like would
  • 00:43:03
    they have similar uh Z manufact
  • 00:43:06
    and another possible applications would
  • 00:43:09
    be uh like what happens to like phone
  • 00:43:10
    online widths do we see any changes in
  • 00:43:13
    phone online widths with magnetic field
  • 00:43:15
    and because we believe that angular
  • 00:43:17
    momentum conservation uh should restrict
  • 00:43:20
    the scattering and the it should narrow
  • 00:43:21
    the language but this is something we
  • 00:43:23
    haven't studied yet and it would also
  • 00:43:26
    provide if it changes like if we can
  • 00:43:28
    control it with magnetic field then it
  • 00:43:30
    will also provide us a mechanism to uh
  • 00:43:32
    tune scattering rates by airplane
  • 00:43:36
    with this I would like to uh thank my
  • 00:43:39
    collaborators my advisor Gregory feed
  • 00:43:41
    from Northeastern University Boston and
  • 00:43:44
    my other collaborators from UT Austin
  • 00:43:46
    talent and University of Tokyo oh thank
  • 00:43:49
    you for your attention
  • 00:44:24
    but that's how you started feeling
  • 00:44:26
    louder
  • 00:44:29
    in the system
  • 00:44:30
    is there any timing with universal
  • 00:44:32
    symmetry in the system
  • 00:44:35
    so in this case there was no emergency
  • 00:44:40
    for the examples that I discussed but
  • 00:44:43
    you can have a situation where you don't
  • 00:44:45
    like where you have inversion
  • 00:44:46
    symmetrical broken
  • 00:44:48
    oh sorry there was inversion submit in
  • 00:44:49
    these systems inversion symmetry was not
  • 00:44:51
    broken but you can have a set of your
  • 00:44:52
    inversion symmetry is broken in that
  • 00:44:54
    case you will get calculus but you will
  • 00:44:56
    get it at some high symmetry points so
  • 00:44:58
    basically you will get title phone one
  • 00:45:00
    at one k point and you will get a
  • 00:45:01
    carophone on it another K point but
  • 00:45:03
    their chirality would be opposing they
  • 00:45:04
    for the overall burial Zone overall
  • 00:45:07
    chirality would feel
  • 00:45:09
    but you can have like at a particular
  • 00:45:11
    moment momentum you can have some kind
  • 00:45:13
    of phone on with the finite card LED
  • 00:45:18
    and that's the case for graphene
  • 00:45:39
    sort of
  • 00:45:43
    strongly affected yeah I tried this
  • 00:45:46
    scattering mechanism would be kind of
  • 00:45:49
    suppressed like if you have these um
  • 00:45:53
    so I think first thing is that would
  • 00:45:55
    depend a lot on the material
  • 00:45:58
    um
  • 00:45:59
    so if you can like design your system in
  • 00:46:02
    a way that now your phone on modes are
  • 00:46:06
    chiral
  • 00:46:07
    like if you let's say apply some
  • 00:46:08
    medicine magnetic field or some other
  • 00:46:10
    time it was limited breaking mechanism
  • 00:46:11
    then I believe that would increase
  • 00:46:15
    electrical conductivity because that
  • 00:46:17
    would decrease the scattered events and
  • 00:46:20
    that should increase
  • 00:46:21
    electronic connectivity yeah
  • 00:46:31
    yeah so that uh so for the scattering
  • 00:46:33
    part that I haven't done
  • 00:46:37
    right right
  • 00:46:40
    by a very large extent
  • 00:46:43
    um
  • 00:46:45
    so I don't have much idea about like I
  • 00:46:49
    haven't Quantified that thing but I
  • 00:46:51
    think there should be a considerable
  • 00:46:52
    effect in fact in that Cupid paper that
  • 00:46:55
    I was showing so for electrical and
  • 00:46:58
    thermal conductivity you have this white
  • 00:46:59
    man friends low so they showed that it's
  • 00:47:02
    violated very strongly in Cube rates and
  • 00:47:05
    they have attributed that effect to
  • 00:47:06
    carry phones I mean they have
  • 00:47:08
    experimentalism but theory-wise uh in
  • 00:47:10
    that paper they haven't Quantified it so
  • 00:47:12
    I don't think there is a mechanism like
  • 00:47:14
    there is any work at this point which
  • 00:47:16
    has considered this kind of
  • 00:47:25
    spiral phonons have a large magnetic
  • 00:47:28
    movement right so and your model is that
  • 00:47:32
    it is sort of coming because of the
  • 00:47:34
    hybridization with the electronic States
  • 00:47:36
    right right so is it possible that one
  • 00:47:39
    is measuring a part of the electronic
  • 00:47:41
    Magnetic Moment itself rather than
  • 00:47:48
    right right that's a very good question
  • 00:47:51
    yeah actually that's what I think what's
  • 00:47:53
    going on because what you are seeing is
  • 00:47:56
    note of your phone on but it's an ad
  • 00:47:57
    mixture
  • 00:47:58
    uh but the thing is like that add
  • 00:48:00
    mixture would be very small like the
  • 00:48:04
    like the sorry the electronic excitation
  • 00:48:07
    percentage would be very small in fact
  • 00:48:09
    in some of my other like I haven't
  • 00:48:11
    presented those with results but we had
  • 00:48:12
    tried to quantify it and it was about 10
  • 00:48:15
    I think for this eg2 phone on like the
  • 00:48:17
    mixing was about 10 because it's
  • 00:48:19
    slightly far from resonance so it's not
  • 00:48:22
    like the hybridization is not very
  • 00:48:24
    strong but there is definitely a very uh
  • 00:48:27
    small like there's definitely this part
  • 00:48:29
    for electronic excitation and now
  • 00:48:31
    electronic excitation has some bore
  • 00:48:32
    magnet on like Magnetic Moment of core
  • 00:48:34
    magnet oil so it's it's possible that
  • 00:48:37
    this 0.1 bore magnetone that you're
  • 00:48:39
    seeing is coming from that glycolic
  • 00:48:41
    excitation
  • 00:48:43
    state that you are measuring right
  • 00:48:54
    because we are quite far away from this
  • 00:48:58
    a level coursing point
  • 00:49:00
    the temperature should
  • 00:49:03
    determine the difference between the two
  • 00:49:05
    right
  • 00:49:06
    should probably die out no but actually
  • 00:49:09
    the energy
  • 00:49:15
    those States come very close to the
  • 00:49:17
    Colony
  • 00:49:20
    because they perhaps have a similar
  • 00:49:21
    temperature
  • 00:49:23
    also like even for the electronic
  • 00:49:25
    excitations like their energy also move
  • 00:49:27
    with magnetic field
  • 00:49:28
    the hybridization amount also changes
  • 00:49:33
    yeah but that's um I think
  • 00:49:46
    which
  • 00:49:48
    means
  • 00:49:49
    yeah but like whatever phononic part you
  • 00:49:51
    will get like it will have like some
  • 00:49:52
    circular motion as you say so I think
  • 00:49:54
    it's okay
  • 00:50:01
    yeah yeah
  • 00:50:05
    so and line with how do they measure if
  • 00:50:09
    at all of the circular kind of thing
  • 00:50:11
    measurement
  • 00:50:18
    I think they did that so we are still
  • 00:50:20
    working out the theory for this language
  • 00:50:22
    actually okay
  • 00:50:23
    [Music]
  • 00:50:26
    yeah I think they just I mean
  • 00:50:28
    experimentally they just measure it from
  • 00:50:30
    here full of half Max
  • 00:50:33
    yeah
  • 00:50:38
    sure yeah but we are as to um
  • 00:50:42
    so how does one actually measure a
  • 00:50:45
    foreign
  • 00:50:47
    ah even let's say Optical novel now
  • 00:50:51
    I don't know
  • 00:50:53
    one is uh definitely Robin experiments
  • 00:50:57
    like you can do that okay
  • 00:50:59
    and I think now I want to see the
  • 00:51:01
    distinction if any
  • 00:51:03
    between the magnitude
  • 00:51:06
    for the one which are twisted
  • 00:51:09
    also I think their temperature
  • 00:51:11
    dependence is very different very
  • 00:51:13
    performance because I'm forgetting the
  • 00:51:15
    name of that thing but you have this and
  • 00:51:17
    harmonic Decay like if you take an
  • 00:51:18
    optical hormone it decays into two um
  • 00:51:21
    acoustic phonons and then you get a very
  • 00:51:24
    peculiar structure from there for
  • 00:51:26
    language and you do that fit into
  • 00:51:28
    temperature and then you can say that
  • 00:51:29
    okay
  • 00:51:31
    and in some cases there can also be like
  • 00:51:33
    some asymmetry but I think it's so it's
  • 00:51:37
    more related to like electrophone on
  • 00:51:39
    coupling like you can have this fanu
  • 00:51:40
    shape kind of thing
  • 00:51:43
    that can also be there and then I think
  • 00:51:45
    that then you can distinguish like
  • 00:51:47
    contributions from black medical
  • 00:51:48
    citation yeah but in this case I think
  • 00:51:51
    it's a good question like if you can
  • 00:51:52
    somehow uh separate the two
  • 00:51:54
    contributions experimentally like what
  • 00:51:57
    is the phononic part and what is
  • 00:51:58
    electronics
  • 00:52:14
    [Applause]
Etiquetas
  • phonons
  • angular momentum
  • magnetic properties
  • chiral phonons
  • orbital-lattice coupling
  • materials science
  • quantum mechanics
  • electronics
  • thermal transport
  • research applications