Virtual Conference December 14 – 16, 2020
Dynamic Quantum Matter and Materials
Organizers: J.T. Haraldsen, University of North Florida A.V. Balatsky, Nordic Institute for Theoretical Physics and The University of Connecticut
We are thankful for the support from the University of North Florida, University of Connecticut, Nordic Institute for Theoretical Physics, and Asia-Pacific Center for Theoretical Physics
December 14 – 16, 2020
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Introduction Quantum matter and materials, like topological states, 2D materials, and Dirac and Weyl materials have grown to be an active area of modern condensed matter. Fascinating properties of quantum materials might lead to technological applications such as spintronics, quantum technologies, and quantum sensors. The combination of new materials discoveries and the development of new probes of quantum matter has helped shape these topics into an exciting area. Recent dynamic and pumped probe experiments reveal a strong promise of Dynamic Quantum Matter as a new research direction. We strive to measure, understand, and predict transient correlations and coherences in quantum materials upon different driving conditions. Therefore, we introduce it as a new topic for this year’s quantum matter conference. We seek to actively discuss hidden, entangled, and dynamic orders that emerge in quantum materials and matter.
The main focus for this upcoming conference will be on the modeling and experimental observations of Dynamic Quantum Matter and Materials (DQMM). Overall, this workshop aims to bring together researchers to discuss and highlight emerging topics and develop ideas for future research.
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Dynamic Quantum Matter and Materials
Contents Introduction ...... 3 Conference Schedule (All times are given in US Eastern Standard Time) ...... 6 Meeting ID: 97365281855 ...... 6 Zoom Passcode: DQMM2020 ...... 6 Monday, December 14 ...... 6 Tuesday, December 15 ...... 7 Wednesday, December 16 ...... 8 Invited Talks ...... 9 Gabriel Aeppli – To be announced ...... 9 Alexander Balatsky – Dynamic and hidden orders in quantum matter / Dynamic orders in quantum matter ...... 9 Annica Black-Schaffer – Josephson effect in Weyl nodal loop semimetals from odd-frequency superconductivity ...... 9 Stefano Bonettii – Driving a soft phonon coherently with intense terahertz fields ...... 10 Ilya Charaev – High-performance large-area single-photon detectors for dark photon search ...... 11 Sinéad M Griffin – The ultimate materials design problem: Designing and maximizing matter couplings to dark matter ...... 12 Chris Hooley – A potential all-electronic route to the charge-density-wave phase in monolayer vanadium diselenide ...... 12 Sergei V. Kalinin – Can (almost) unsupervised machine learning learn physics of quantum materials from atomically-resolved imaging data? ...... 13 Jonathan Keeling – Crescent states in charge-imbalanced polariton condensates ...... 14 Adriana Moreo – Block magnetism and orbital-selective correlations in low-dimensional iron-based superconductors ...... 14 Bart Olsthoorn – Barcodes for spin models ...... 15 Henrik Schou Røising – Axion-matter coupling in multiferroics ...... 15 Ilya Sochnikov – Strain-driven domain physics in a ferromagnetic Weyl semimetal revealed by scanning SQUID microscopy ...... 15 Nicola Spaldin – How hidden magnetoelectric multipolar order can't stay hidden at surfaces...... 16 Jian-Xin Zhu – Understanding Magnetism, Ferroelectricity, and Non-equilibrium Quantum Physics via Machine Learning ...... 16 Posters ...... 17
December 14 – 16, 2020
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Dynamic Quantum Matter and Materials
1) Amelia Brumfield – Evolution of the quantum phase transitions in XXY general spin trimers with applied magnetic field and variable exchange parameters ...... 17 2) Abigail A. Coker – Effects of spin rotation on the spin dynamics of the 120-degree phase in the Kagome lattice ...... 17 3) Benedikt Fauseweh – Laser pulse driven nonequilibrium dynamics in the Kondo lattice model .. 18 4) Thomas Harrelson – Understanding Phonon Decoherence in Materials used in the Search for sub- GeV Dark Matter ...... 19 5) Satya K. Kushwaha – Metallization and Fermi-liquid state in a Kondo-insulator in high magnetic fields ...... 19 6) Aditi D. Mahabir – Negative electronic compressibility in multi-band 2D electron gases with
application to LaAlO3/SrTiO3 ...... 20 7) Jose Pagan – Spin-dynamics of the Lieb lattice with variable exchange parameters ...... 20 8) Joris Schaltegger – Bose-Einstein condensates of Dirac magnons ...... 20 9) Pavlo Sukhachov – Acoustogalvanic effect in Weyl and Dirac semimetals ...... 21 List of Registered Participants ...... 22 Note Pages ...... 24
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Conference Schedule (All times are given in US Eastern Standard Time) Meeting ID: 97365281855 Zoom Passcode: DQMM2020 Monday, December 14
Session I – Dynamic Matter and Coherent Orders
9:45 a.m. – Zoom Session is Opened Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09 9:55 a.m. – Introduction – Jason T. Haraldsen – University of North Florida
10:00 – 10:15 a.m. – Alexander Balatsky – Dynamic and Hidden Orders in Quantum Matter 10:15 – 10:30 a.m. – Jonathan Keeling – Crescent States in Charge-Imbalanced Polariton Condensates 10:30 – 10:45 a.m. – Stefano Bonetti – Driving a soft phonon coherently with intense terahertz fields 10:45 – 11:00 a.m. – Gabriel Aeppli – To be announced 11:00 – 12:00 p.m. – Panel Discussion on the Topic
12:00 – 2:00 p.m. – Open Time 12:30 – 1:30 p.m. – Virtual Poster Session and Open Forum (Zoom Break Rooms – See Poster Section) Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
Session II – Novel Orders in Quantum Matter
1:45 p.m. – Zoom Session is Opened Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
2:00 – 2:15 p.m. – Annica Black-Schaffer – Josephson effect in Weyl nodal loop semimetals from odd-frequency superconductivity 2:15 – 2:30 p.m. – Nicola Spaldin – How hidden magnetoelectric multipolar order can't stay hidden at surfaces 2:30 – 2:45 p.m. – Chris Hooley – A potential all-electronic route to the charge-density-wave phase in monolayer vanadium diselenide 2:45 – 3:00 p.m. – Adriana Moreo – Block magnetism and orbital-selective correlations in low-dimensional iron-based superconductors 3:00 – 4:00 p.m. – Panel Discussion on the Topic
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Tuesday, December 15
Session III – Quantum Materials for Dark Matter Detection
9:45 a.m. – Zoom Session is Opened Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
10:00 – 10:15 a.m. – Ilya Sochnikov – Strain-Driven Domain Physics in a Ferromagnetic Weyl Semimetal Revealed by Scanning SQUID Microscopy 10:15 – 10:30 a.m. – Henrik Schou Røising – Axion-matter coupling in multiferroics 10:30 – 10:45 a.m. – Sinéad M Griffin – The Ultimate Materials Design Problem: Designing and Maximizing Matter Couplings to Dark Matter 10:45 – 11:00 a.m. – Ilya Chareav – High-performance large-area single-photon detectors for dark photon search 11:00 – 12:00 p.m. – Panel Discussion on the Topic
12:00 – 2:00 p.m. – Open Time 12:30 – 1:30 p.m. – Virtual Poster Session and Open Forum (Zoom Break Rooms – See Poster Section) Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
Session IV – Quantum Materials and Machine Learning
2:00 p.m. – Zoom Session is Opened Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
2:15 – 2:30 p.m. – Bart Olsthoorn – Barcodes for spin models 2:30 – 2:45 p.m. – Sergei V. Kalinin – Can (almost) unsupervised machine learning learn physics of quantum materials from atomically-resolved imaging data? 2:45 – 3:00 p.m. – Jian-Xin Zhu – Understanding Magnetism, Ferroelectricity, and Non- equilibrium Quantum Physics via Machine Learning 3:00 – 4:00 p.m. – Panel Discussion on the Topic
December 14 – 16, 2020
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Wednesday, December 16
Session V – Asia-Pacific Forum
7:45 a.m. – Zoom Session is Opened Join Zoom Meeting https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
8:00 – 9:00 a.m. – Alexander Balatsky – Dynamic orders and quantum matter
Session VI – Group Meeting
Time to be determined – Group Meeting
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Invited Talks
Gabriel Aeppli – To be announced Paul Scherrer Institute – Villigen, Switzerland TBA
Alexander Balatsky – Dynamic and hidden orders in quantum matter / Dynamic orders in quantum matter Nordic Institute for Theoretical Physics – Stockholm, Sweden University of Connecticut – Storrs, Connecticut, USA
Quantum matter out of equilibrium emerge as an important platform to induce correlations and transient orders. Broad basic questions about orders that are inherently dynamic have been addressed in the context of driven cold atoms, spins, magnetic states and superconductors. I will discuss the example of emergent dynamic and entangled states in quantum paralelectrics where driven electric fluctuations induce magnetization, the dynamic multiferroicity phenomenon [1]. We see a rapidly growing list of unusual quantum states in time domain to be discovered. I will point to other examples of dynamic orders out of equilibrium, e.g. coherent states of magnons in Dirac materials [2]. [1] Dynamic multiferroicity of a ferroelectric quantum critical point, K Dunnett, JX Zhu, NA Spaldin, V Juričić, AV Balatsky, Physical review letters 122 (5), 057208 (2020); Dynamical multiferroicity, DM Juraschek, M Fechner, AV Balatsky, NA Spaldin, Physical Review Materials 1 (1), 014401(2017). [2] Bose-Einstein condensate of Dirac magnons: pumping and collective modes, PO Sukhachov, S Banerjee, AV Balatsky, arXiv preprint arXiv:2008.01328 (2020)
Annica Black-Schaffer – Josephson effect in Weyl nodal loop semimetals from odd-frequency superconductivity Uppsala University – Uppsala, Sweden
Weyl nodal loop semimetals (WNLs) host a closed nodal line loop Fermi surface in the bulk and protected zero-energy flat band, or drumhead, surface states that are fully spin- polarized. The large density of states of the drumhead states makes WNLs exceedingly prone to electronic ordering. At the same time, the spin-polarization naively prevents conventional superconductivity due to its spin-singlet nature. Here we show the complete opposite: WNLs are extremely promising materials for superconducting Josephson junctions, entirely due to odd-frequency superconductivity. By sandwiching a WNL between two conventional superconductors we theoretically demonstrate the presence of extremely large Josephson currents, even up to orders of magnitude higher than for normal metals. The large currents are generated by an efficient transformation of spin- singlet pairs into odd-frequency equal-spin pairing as well as the drumhead states ensuring an exceptionally strong proximity effect.
December 14 – 16, 2020
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Stefano Bonettii – Driving a soft phonon coherently with intense terahertz fields Stockholm University – Stockholm, Sweden
In recent years, the development of femtosecond laser sources with tunable wavelength in the mid- and far-infrared regime has enabled novel experiments where it was possible to achieve resonant driving of collective excitations in solids, such as phonons. The interest in this kind of studies is driven by the opportunity of not only understanding, but also controlling the properties of matter with intense light fields. The broad goal of these investigations is to drive materials into states that are not attainable in thermodynamic equilibrium. In this short talk, I will present our recent experimental results where we used strong single-cycle terahertz fields to coherently drive the soft phonon mode of an archetypal perovskite, strontium titanate. Femtosecond X-ray diffraction reveals that these types of excitations are able to drive the soft phonon mode in nonlinear regimes, leading to coupling to phonon modes with much higher energy. With near-infrared probes, direct access to lattice motion is precluded due to the long wavelength. However, collective excitations can still be detected and, furthermore, table-top setups allow to investigate in detail the role of the pump polarization and the detection geometry to characterize the full response of the sample.
December 14 – 16, 2020
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Ilya Charaev – High-performance large-area single-photon detectors for dark photon search Massachusetts Institute of Technology – Boston, Massachusetts, USA Ilya Charaev1, Yukimi Morimoto1, Marco Colangelo1, Akshay Agarwal1, Karl K. Berggren1, Jeffrey Chiles2, Varun Verma2, Sae Woo Nam2, Asimina Arvanitaki3, Junwu Huang3, Masha Baryakhtar4, Ken Van Tilburg4,5, Robert Lasenby6, Yonit Hochberg7 1Massachusetts Institute of Technology, 50 Vassar Street, Cambridge, MA 02139 2National Institute of Standards and Technology, 100 Bureau Drive Gaithersburg, MD 20899 3Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Canada, N2L 2Y5 4New York University, 70 Washington Square South, New York, NY 10012 5Institute for Advanced Studies, 1 Einstein Drive Princeton, NJ 08540 6Stanford University, 450 Serra Mall, Stanford, CA 94305 7Hebrew University of Jerusalem, Mt. Scopus, Jerusalem, 9190501, Israel
We present recent results on the design, fabrication, and testing of nano- and micro-scale WSi and MoSi superconducting nanowire single-photon detectors for detecting bosonic dark matter particle candidates. In this experiment, we look for dark matter (such as dark photons) with mass energies in the range of 10 meV to 10 eV. Detectors may be combined with gas cells, dielectric stacks [1], or combinations of these structures in cryogenic targets, optimized for dark matter absorption. Furthermore, superconducting nanowires are used as both target and sensor for direct detection of sub-GeV dark matter [2]. We report our measurements of the count rate of the nanowires coupled to the dark matter resonator. Our latest measurements had 3 dark counts during an integrated run time of 84 h 17 min. This count rate is consistent with estimated count rate from background natural radioactivity and cosmic-ray muons. Future experiments using SNSPDs should enable probing new territory in the detection landscape, establishing the complementarity of this approach to other dark matter search experiments. [1] M. Baryakhtar, J. Huang, and Robert Lasenby, Phys. Rev. D 98, 035006, 2018. [2] Y. Hochberg, I. Charaev, S.-W. Nam, V. Verma, M. Colangelo, K. K. Berggren, Phys. Rev. Lett. 123, 151802, 2019.
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Sinéad M Griffin – The ultimate materials design problem: Designing and maximizing matter couplings to dark matter Lawrence Berkeley National Laboratory – Berkeley, California, USA
Dark matter (DM) is estimated to make up ~85% of the mass density of the universe, however, despite concerted efforts it has so far evaded detection. New ideas for detecting well-motivated DM candidates are needed that (i) push the sensitivity of detectors to lower masses than currently available and/or (ii) that maximize the interaction cross section with DM models. In this talk I will discuss how excitations in quantum materials are a natural place to investigate routes to DM detection owing to the match of energy scales for sub- GeV DM candidates, and the recent strides in synthesis, characterization and theoretical understanding of excitations in these materials. In particular, I will discuss how the coupling of DM to polar, topological and magnetic materials can be estimated using first- principles calculations, and how materials design can be used to optimize these cross- section amplitudes to suggest the target materials for next-generation sub-GeV dark matter detectors.
Chris Hooley – A potential all-electronic route to the charge-density-wave phase in monolayer vanadium diselenide University of St. Andrews – St. Andrews, United Kingdom
We present a potential mechanism for charge-density-wave formation in monolayers of the transition metal dichalcogenide 1T-VSe2 in which the key role in the low-energy phase competition is played by a combination of electron-electron interactions and nesting. Via a renormalization group treatment of an effective extended Hubbard model we examine the competition of superconducting and density-wave fluctuations as sections of the Fermi surface are tuned to perfect nesting. We find regions of charge-density-wave order when the effective Heisenberg exchange interaction is comparable to the effective Coulomb repulsion, and d-wave superconductivity when all effective interactions are purely repulsive. We discuss the possible role of lattice vibrations in enhancing the effective Heisenberg exchange during the earlier stages of the renormalization group flow.
December 14 – 16, 2020
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Sergei V. Kalinin – Can (almost) unsupervised machine learning learn physics of quantum materials from atomically-resolved imaging data? Oak Ridge National Laboratory – Oak Ridge, Tennessee, USA
Rich functionalities of quantum and strongly correlated materials emerge from the interplay between the electronic, orbital, lattice, and spin degrees of freedom that often lead to complex structural and electronic phenomena spanning atomic to mesoscopic scales. In many cases, these phenomena are associated with translational symmetry breaking, local frozen disorder, or strongly correlated disorder. However, the relevant mechanisms and roles of individual subsystems often remain unknown. Over the last decade, Scanning Transmission Electron Microscopy has emerged as a powerful quantitative probe of materials structure on the atomic level, providing high veracity information on local chemical bonding, composition, and symmetry breaking distortions. We aim to harness the power of machine learning methods to build a comprehensive picture of the chemistry and physics of quantum materials from these observations. In this presentation, I will illustrate an approach for the recovery of generative models (i.e. microscopic lattice Hamiltonian) from the atomically resolved imaging data, as well as exploration of local symmetry-breaking phenomena. I will further illustrate the applications of the Bayesian inference methods towards inferring the mesoscopic and atomistic physics of materials and illustrate the pathways towards incorporation of physical models as priors within Bayesian optimization towards effective sampling of experimental parameter spaces. Ultimately, we seek to answer the questions such as whether frozen atomic disorder drives the emergence of the local structural distortions or average shift of the Fermi level induces structural reconstruction that in turn drive cation distribution, whether the nucleation spot of phase transition can be predicted based on observations before the transition, and what is the driving forces controlling the emergence of unique functionalities in quantum materials.
This research is supported by the by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division and the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, BES DOE.
December 14 – 16, 2020
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Jonathan Keeling – Crescent states in charge-imbalanced polariton condensates University of St. Andrews – St. Andrews, United Kingdom
We studied two-dimensional charge-imbalanced electron-hole systems embedded in an optical microcavity. We found that strong coupling to photons favors states with pairing at zero or small center-of-mass momentum, leading to a condensed state with spontaneously broken time-reversal and rotational symmetry and unpaired carriers that occupy an anisotropic crescent-shaped sliver of momentum space. I will discuss the phase diagram of this system, and some open questions raised by this work.
This work was in collaboration with Artem Strashko (Flatiron Institute, NY), Francesca Marchetti (UA Madrid), and Allan MacDonald (UT Austin): Phys. Rev. Lett. 125, 067405 (2020). https://doi.org/10.1103/PhysRevLett.125.067405
Adriana Moreo – Block magnetism and orbital-selective correlations in low- dimensional iron-based superconductors University of Tennessee and Oak Ridge National Laboratory – Knoxville/Oak Ridge, Tennessee, USA
New directions towards our understanding of pairing tendencies in iron-based superconductors have emerged from the discovery of superconductivity in Fe-based two- leg ladder materials under high pressure [1]. Strongly correlated multi-orbital systems in quasi one dimension can be studied with great accuracy with computational techniques. Numerical methods such as DMRG allow the study of multi-orbital Hubbard models at various Hubbard and Hund couplings, and electronic densities. Via these approaches we have found clear indications of pairing in slightly doped chains [2] and ladders [3]. In addition, we have found that these systems have very rich magnetic properties; in particular they exhibit an “orbital selective Mott Phase” in a wide range of parameters. This phase is characterized by magnetic block states in which a block of N spins “up” alternate with a block of N spins “down” [4,5,6,7]. We were able to calculate the dynamical spin structure factor and interpret the results in terms of a mixture of acoustic and optical modes [4,6,7] also observed in neutron scattering experiments. The complex behavior observed from accurate studies of models for the Fe-based superconductors in one dimension indicates that the physics of these materials could unveil unexpected surprises. [1] H. Takahashi et al., Nat. Mater. 14, 1008 (2015); J. Ying et al., PRB 95, 241109(R) (2017). [2] N. Patel et al., PRB 96, 024520 (2017) [3] N. Patel et al., PRB 94, 075119 (2016) [4] J. Herbrych et al., Nat. Comm. 9, 3736 (2018) [5] J. Herbrych et al., PRL 123, 027203 (2019) [6] J. Herbrych et al., PNAS 117, 16226 (2020) [7] J. Herbrych et al., Phys. Rev. B 102, 115134 (2020). Work supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
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Bart Olsthoorn – Barcodes for spin models Nordic Institute for Theoretical Physics – Stockholm, Sweden
Spin models can have complicated phase diagrams that are hard to characterize without knowing the order parameter. We show that persistent homology – a relatively new field in applied mathematics – can be used as a general approach to uncover a phase diagram, involving a concept called barcodes. We also demonstrate this for the XXZ model (on the pyrochlore lattice) and automatically identify all six phases, including hidden phases such as the spin-ice phase.
Henrik Schou Røising – Axion-matter coupling in multiferroics Nordic Institute for Theoretical Physics – Stockholm, Sweden
Multiferroics are materials with two or more ferroic orders, like spontaneous ferroelectric and ferromagnetic polarizations. Such materials often exhibit a magnetoelectric (ME) effect whereby magnetic and electric polarizations couple linearly, reminiscent of the electrodynamic axion coupling. In this talk I will explore the possibility of external (dark matter) axions coupling to ferroic orders in these materials. For a linear ME effect the magnetic response is perturbed to linear order in the axion coupling. At temperatures close to the ferromagnetic transition, I will discuss how fluctuations can lead to a relative enhancement of the axion-induced magnetic response.
Ilya Sochnikov – Strain-driven domain physics in a ferromagnetic Weyl semimetal revealed by scanning SQUID microscopy University of Connecticut – Storrs, Connecticut, USA
Magnetic Weyl semimetals are predicted to host emergent electromagnetism at heterogeneously strained phases or at the magnetic domain walls. Tunability and control of the topological and magnetic properties is crucial for revealing these phenomena. Here, we use a scanning SQUID microscope to image spontaneous magnetization and magnetic susceptibility of CeAlSi, a noncentrosymmetric ferromagnetic Weyl semimetal candidate. We observe large metastable domains alongside stable ferromagnetic domains. We find evidence that the heterogeneity of the two types of domains arises from magnetoelastic or magnetostriction effects. We show how these domains form, how they interact, and how they can be manipulated or stabilized with estimated lattice strains on picometer levels. Proposed future applications of strain-tuned and magnetically tuned Dirac materials are many. One interesting direction is applying these materials to Dark matter detection. We will discuss why materials like ours and knowledge about their tunability may be relevant to the search for the exotic matter.
December 14 – 16, 2020
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Dynamic Quantum Matter and Materials
Nicola Spaldin – How hidden magnetoelectric multipolar order can't stay hidden at surfaces. Eidgenössische Technische Hochschule Zürich – Zürich, Switzerland
We show that linear magnetoelectric materials -- in which an applied electric field induces a linear magnetization and vice versa -- have an intrinsic surface magnetic dipole moment that is analogous to the bound surface charge in ferroelectric materials. This surface magnetic dipole moment can be conveniently described in terms of a bulk magnetoelectric multipolization that is analogous to the ferroelectric polarization. We provide a convenient recipe for extracting the surface magnetic dipole moment for any surface plane given the bulk magnetic order, demonstrating the procedure for the prototypical magnetoelectric material, Cr2O3. Finally, we discuss practical implications and routes to experimental verification.
Jian-Xin Zhu – Understanding Magnetism, Ferroelectricity, and Non-equilibrium Quantum Physics via Machine Learning Los Alamos National Laboratory – Los Alamos, New Mexico, USA
Data driven approaches based on machine learning (ML) algorithms have gained much popularity in the domain of physical science as tools for accelerating both fundamental and applied research. A general analytical framework combining such algorithms with existing data can be used to explore the structure-property-performance relationship in a wide range of material systems. This talk will be focused on reviewing three such cases where ML algorithms and statistical techniques, coupled with materials data obtained from simulations or experiments, are employed to construct comprehensive ML-based models capable of predicting complex materials behavior. Specifically, we investigate (i) strength and ordering of magnetic moments in actinide-based compounds, (ii) occurrence of ferroelectricity in molecular entities and (iii) capabilities of ML in learning non-equilibrium physics even in quantum systems. All such applications adopt uniform approach to data curation and construction of ML models following supervised and unsupervised learnings as applicable.
This work was carried out under the auspices of the U.S. DOE NNSA (Contract No. 89233218CNA000001) and was supported by the LANL LDRD Program.
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Posters Posters will be in individual breakout rooms on Zoom. To see the posters and talk with presenters, please click on the poster session link and choose the appropriate breakroom number. To easily move between breakrooms, please update your Zoom application to the newest version.
Posters will be presented on both days. Poster Session I (Monday) - https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09 Poster Session II (Tuesday) - https://unf.zoom.us/j/97365281855?pwd=ZjBEMjZRMU14SGY5U0FMcjB6RWIrQT09
Additional Breakout Rooms are available for individual discussion or meetings or if you would like to present your own work.
1) Amelia Brumfield – Evolution of the quantum phase transitions in XXY general spin trimers with applied magnetic field and variable exchange parameters University of North Florida – Jacksonville, Florida, USA
This study investigates the thermodynamics and magnetic excitations of XXY general spin isosceles quantum trimers with a variable magnetic field and exchange parameters. Using an isotropic Heisenberg Hamiltonian, we analyze how the energy eigenstates, heat capacities, and magnetic susceptibilities evolve in mixed asymmetric systems of with exchange parameters of J1 and J2. Our analysis of these states' evolution allows us to map out the quantum phase transitions in these spin systems. From our findings, we hope to provide further insight into the general understanding of molecular magnet systems with an increase in different parameters and useful characterization methods of experimental investigations of molecular magnets and spin clusters.
2) Abigail A. Coker – Effects of spin rotation on the spin dynamics of the 120-degree phase in the Kagome lattice University of North Florida – Jacksonville, Florida, USA
We examine the effect of distorted triangular magnetic interactions in the Kagome lattice on the spin-wave dynamics. Using a Holstein-Primakoff expansion of the Heisenberg Hamiltonian, we determine the analytical solutions for the various magnetic configurations of the Kagome. Through an understanding of the magnetic phase diagram, we characterize the changes in the spin-waves and examine the distortion of the 120-degree phase with variable exchange interactions. The goal of this work is to gain a general understanding of the magnetic fingerprint for these configurations for experimental methods and identification.
December 14 – 16, 2020
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3) Benedikt Fauseweh – Laser pulse driven nonequilibrium dynamics in the Kondo lattice model Los Alamos National Laboratory – Los Alamos, New Mexico, USA
Experimental advances in nonlinear optics and ultrafast spectroscopy allow for unprecedented access to nonequilibrium physics of strongly correlated materials. By using this approach, many new and exciting phenomena have been discovered in recent years. Heavy fermion systems are one prototypical class of strongly correlated materials. The interplay between localized magnetic moments and conduction electrons are the driver behind unconventional superconductivity, magnetic order and quantum criticality. The Kondo lattice model is used to describe the emergent phenomena of such systems. By using the powerful time-dependent variational Monte Carlo (tVMC) method, we investigate the nonequilibrium dynamics of the model after strong laser excitation. Focusing on the quarter filled case, where a charge density wave is coexisting with antiferromagnetic spin order, we demonstrate that the spin and charge fluctuations can be manipulated by varying shape and intensity of the laser pulse. The charge and spin dynamics is tracked by calculating the time-dependent structure factors within the tVMC framework. Strong laser pulses allow us to dynamically suppress the charge order completely in favor of the spin order, thus driving the system into a new phase, which is not accessible by thermal fluctuations. Strong changes in the time evolution of double occupancy and momentum distribution also indicate a dynamical transition from an insulating to a conducting state. Additionally, we show, that the current induced by the pump pulse shows strong non-linearities, depending on the suppression of charge order. This has a pronounced effect in the higher harmonic generation spectrum (HHG), which can be accessed experimentally. Our work shows that laser pulse driven heavy fermion system can excite non-thermal coherent states, which can alter the fundamental properties of materials.
December 14 – 16, 2020
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4) Thomas Harrelson – Understanding Phonon Decoherence in Materials used in the Search for sub-GeV Dark Matter Lawrence Berkeley National Laboratory – Berkeley, California, USA
Searching for dark matter particles with masses lower than 1 GeV requires detecting excitations on the meV scale. At this scale, quasiparticles in condensed matter systems like phonons, magnons, and excitons are the dominant carriers of information. However, given the weak interactions between these quasiparticles and dark matter, in addition to their generally short lifetimes, the efficient extraction of information about DM-matter interactions is difficult. As a result, it is critical to understand the decoherence mechanisms of the variety of quasiparticle distributions in materials that can be used as targets in direct detection experiments so they can be understood and potentially mitigated. For phonons, these decoherence mechanisms are broken into three categories: anharmonic, isotopic, and surface scattering. We use first principles calculations to determine each scattering rate for a variety of potential dark matter target materials that can be used in future direct detection experiments. These calculations reveal which decoherence mechanisms dominate for different phonon energies, providing insight into which material combinations work best for phonon-based direct detection experiments.
5) Satya K. Kushwaha – Metallization and Fermi-liquid state in a Kondo-insulator in high magnetic fields Los Alamos National Laboratory – Los Alamos, New Mexico, USA
Kondo insulators are a class of quantum materials in which the coupling between conduction electrons and nearly localized f-electrons which are expected to transform into metals under strong magnetic field. The closure of insulating gap required strong magnetic field typically of order 100 T, therefore, a very little is known about this transition. Here we present a systematic study of insulator-metal transition and a Fermi-liquid state in Ce3Bi4Pd3 under strong magnetic fields of 65 T. Titled results are established by our charge transport and magnetization experiments in the strong magnetic fields at pulsed field facility at NHMFL Los Alamos.
Kushwaha, S.K. et al., Magnetic field-tuned Fermi liquid in a Kondo insulator, Nat Comm. 10, 5487 (2019).
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6) Aditi D. Mahabir – Negative electronic compressibility in multi-band 2D electron gases with application to LaAlO3/SrTiO3 University of Connecticut – Storrs, Connecticut, USA
We investigate the effects of a two-band model in the description of the negative electronic compressibility (NEC) for the two-dimensional electron gas (2DEG). Using a homogeneous 2D interacting electron model, we examine the crossover point of the electronic compressibility of the 2DEG with one and two electron bands and find that the presence of inter-band coupling produces a dramatic decrease in the effective dielectric constant and the critical carrier density of the 2DEG. Furthermore, we investigate how these parameters change with variable effective mass. Additionally, we apply our results to the NEC observed in the 2D electron gas at the interface of LaAlO3/SrTiO3 (LAO/STO) and demonstrate how one can observe effects of inter-band interactions in electronic compressibility. We determine that for the known parameters of LAO/STO, the system may be a realization of two-band 2D electron gas.
7) Jose Pagan – Spin-dynamics of the Lieb lattice with variable exchange parameters University of North Florida – Jacksonville, Florida, USA
In this poster, we discuss the effects of variable exchange interactions on the spin dynamics of the Lieb lattice. Using a Holstein-Primakoff expansion of the Heisenberg Hamiltonian, we determine the magnetic phase diagram for various magnetic configurations as well as the spin-wave dynamics with multiple nearest-neighbor and next-nearest-neighbor interactions. We also discuss the evolution of a Lieb lattice transforming into a Kagome lattice and how the accompanying respective magnetic configurations change during this process, and whether they remain stable.
8) Joris Schaltegger – Bose-Einstein condensates of Dirac magnons Nordic Institute for Theoretical Physics – Stockholm, Sweden
Parametrically pumped Dirac magnons can potentially form a Bose-Einstein condensate at the Dirac points. This novel type of material combines the physics of driven-dissipative Bose-Einstein condensates with the non-trivial topology of the Dirac point. Based on a microscopic model of a honeycomb ferromagnet with Kitaev interactions, a phenomenological free-energy density for the condensate is proposed. For homogeneous solutions, Rabi oscillations are observed between the condensates on different sublattices. The non-trivial topology is manifest in the existence of steady-state vortex solutions.
December 14 – 16, 2020
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9) Pavlo Sukhachov – Acoustogalvanic effect in Weyl and Dirac semimetals Yale University – New Haven, Connecticut, USA
The effects of dynamical strain-induced pseudo-electromagnetic fields in Dirac and Weyl semimetals are discussed. The acoustogalvanic effect is proposed as a nonlinear mechanism to generate a direct electric current by passing acoustic waves in Dirac and Weyl semimetals. Unlike the standard acoustoelectric effect, which relies on the sound- induced deformation potential and the corresponding electric field, the acoustogalvanic one originates from the pseudo-electromagnetic fields, which are not subject to screening. Because of the interplay of pseudoelectric and pseudomagnetic fields, the current could show a nontrivial dependence on the direction of sound wave propagation. Being within the experimental reach, the effect can be utilized to probe dynamical deformations and corresponding pseudo-electromagnetic fields, which are yet to be experimentally observed in Weyl and Dirac semimetals.
December 14 – 16, 2020
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List of Registered Participants First Name Last Name Affiliation David Abergel Nature Physics Gabriel Aeppli Paul Scherrer Institut (PSI) Alexander Balatsky Nordic Institute for Theoretical Physics (NORDITA) Sumanta Bandyopadhyay Nordic Institute for Theoretical Physics (NORDITA) Yunkyu Bang Asia-Pacific Center for Theoretical Physics National Institute of Science Education and Braj Bhusan Singh Research, Bhubaneswar, India Annica Black-Schaffer Uppsala University Stefano Bonetti Stockholm University Adrien Bouhon Nordic Institute for Theoretical Physics (NORDITA) Amelia Brumfield University of North Florida David Carvalho Nordic Institute for Theoretical Physics (NORDITA) Ilya Charaev Massachusetts Institute of Technology Alla Chikina Aarhus University Abigail Coker University of North Florida Davide Curcio Aarhus University Paramita Dutta Uppsala University Timon Emken Chalmers University of Technology Tobias Esswein Eidgenössische Technische Hochschule (ETH) Zürich Paulina Ewa Majchrzak Aarhus University Javad Farrokhi University of North Florida Benedikt Fauseweh Los Alamos National Laboratory Benjo Fraser Nordic Institute for Theoretical Physics (NORDITA) Ayana Ghosh Oak Ridge National Laboratory Sinead Griffin Lawrence Berkley Laboratory Jason Haraldsen University of North Florida Thomas Harrelson Lawrence Berkeley National Laboratory Philip Hofmann Aarhus University Chris Hooley St. Andrews University Kasturie Jatkar Stockholm University Sergei Kalinin Oak Ridge National Laboratory Jonathan Keeling St. Andrews University Satya Kushwaha Los Alamos National Laboratory Dushko Kuzmanovski Nordic Institute for Theoretical Physics (NORDITA) W. Brian Lane University of North Florida Long Liang Nordic Institute for Theoretical Physics (NORDITA) Aditi Mahabir University of Connecticut Marek Matas Eidgenössische Technische Hochschule (ETH) Zürich
December 14 – 16, 2020
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Adriana Moreo University of Tennessee Iryan Na University of California, Berkeley Bart Olsthoorn Nordic Institute for Theoretical Physics (NORDITA) Jose Pagan University of North Florida Thomas Pekarek University of North Florida Henrik Roising Stockholm University Filip Ronning Los Alamos National Laboratory Charlotte Sanders UK Central Laser Facility Joris Schaltegger Nordic Institute for Theoretical Physics (NORDITA) Ranjani Seshardri Ben Gurion University Ilya Sochnikov University of Connecticut Nicola Spaldin Eidgenössische Technische Hochschule (ETH) Zürich Pavlo Sukhachov Yale University Einar Urdshals Chalmers University of Technology Gregory Wurtz University of North Florida Yu Zhang UK Central Laser Facility Jian-Xin Zhu Los Alamos National Laboratory
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Note Pages
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