Condensed Matter Seminars

Condensed Matter
Thursday, April 21, 2022
3:30 PM
Clark Hall, Room G004

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"Transport on an interacting helical edge with resonant impurities"


Youjian Chen , University of Virginia - Department of Physics
[Host: Prof. Dima Pesin]
ABSTRACT:

The  quantum  spin  Hall  insulator, also  known  as  a  two-dimensional  (2D) topological  insulator,  is  a  topological  state  of  matter  supporting  the  helical edge states, which are counter-propagating, spin-momentum locked 1D modes protected  by  time  reversal  symmetry. It  exhibits  special  magneto-transport properties under external magnetic field. In my talk, I will construct modified Anderson impurity models to study the magneto-conductance of the quantum spin hall insulator. Firstly, I will solve the transmission through single impurity on helical Luttinger liquid in the presence of magnetic field using Lippmann-Schwinger equation.  I will show the analytical expression for trans- mission and reflection coefficient in terms of the difference between energy of particle and the impurity level, the hybridization coefficient and the magnetic field. Then, I will show the effect of Coulomb interaction on helical Luttinger liquid at Hartree-Fock level. Using renormalization group, I will derive the temperature dependence of conductance.  Lastly, I will show the coherent transport of transmission through many impurities with different energy and hybridization coefficient in the presence of magnetic field.  I will compare my theoretical result with experiment.

Condensed Matter
Thursday, April 14, 2022
4:00 PM
Clark Hall, Room G004
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"Probing correlations in fermionic triangular Hubbard systems"


Jirayu Mongkolkiattichai , University of Virginia - Department of Physics
[Host: Prof. Peter Schauss]
ABSTRACT:

Quantum gas microscopes have expanded the understanding of many-particle physics with their unique ability of single atom resolved imaging. Quantum gas microscopes provide microscopic information of quantum many-body states through spatial correlation functions. Relying on the unique tunability of ultracold atoms in atomic interactions via Feshbach resonances, density, and spin-imbalance, we study a wide parameter range in the phase diagram. Interestingly, a triangular lattice is the simplest example of geometric frustration because three spins with antiferromagnetic interactions cannot be antiparallel, leading to large degeneracies in the many-body ground state [1]. In this talk, I present a Mott insulator of lithium-6 on a symmetric triangular lattice with a lattice spacing of 1003 nm. The lattice is imaged via a Raman sideband cooling technique with imaging fidelity of 98% [2]. We calibrated tunneling by extracting lattice depth from band excitation and the interaction is determined using doublon formation. We can access single-species singles components with the use of doublon hiding [3] and spin removal techniques [4] to detect spin-spin correlations. We compare the results to Determinantal Quantum Monte Carlo calculations, plan to investigate 120° Neel ordering in Heisenberg antiferromagnets, and search for quantum spin liquids in the triangular lattice Hubbard system.

[1] L. Balents, Nature 464, 7286 (2010).

[2] J. Yang, et al., PRX Quantum 2, 020344 (2021).

[3] P. T. Brown, et al., Science 357, 6358 (2017).

[4] M. F. Parsons, et al., Science 353, 1253 (2016). 

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Thursday, April 7, 2022
2:30 PM
Clark Hall, Room G004
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"Driven Majorana Zero Modes: A Route to Synthetic px+ipy Superconductivity"


Lingyu Yang , University of Virginia - Department of Physics
[Host: Prof. Gia-Wei Chern]
ABSTRACT:

In the Kitaev's toy model with a constant chemical potential, the Majorana zero modes (MZMs) can exist but stay localized at the edges of a 1D spinless chain. In this talk, I will introduce the Kitaev's toy model with a site-dependent chemical potential. In this case, one is able to create segments of topological and normal superconducting phases. The MZMs exist at the domain walls between the two phases, but not necessarily at the edges of the whole chain. By tuning the chemical potential such that the domain walls can change in space, the MZMs are able to move in space as well. We call this motion of MZMs the Majorana pump and argue that it leads to px+ipy superconductivity. I will present how the py pairing emerges, and how to realize this model in experiments.

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Thursday, February 24, 2022
3:30 PM
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"Seas of Spin liquids: a glimpse from Kitaev Model"


Professor G. Baskaran , The Institute of Mathematical Sciences and IIT Madras, India; Perimeter Institute for Theoretical Physics, Waterloo, Canada
[Host: Prof. Bellave Shivaram]
ABSTRACT:

P.W. Anderson envisaged a novel situation of quantum paramagnetic (quantum spin liquid) phase of low spin Mott insulators, back in 1973 and described it using Pauling's  resonating valence bonds states. RVB idea got a resurgence, with the discovery of high Tc superconductivity by Bednorz and Muller in 1986. Low dimensionality and frustrations enhance quantum fluctuations in low spin systems, resulting in a variety of spin liquids and many ideas -  emergent gauge fields, Majorana Fermi sea, to topological phases etc. I will discuss a delightful and exactly solvable model by Kitaev, which realized dreams of RVB theorists and more, in an exact fashion. This fertile model is experimentally realized now, thanks to Khaliullin and Jackeli's prediction. There are continuing surprises, including very recent discovery of anomalous non-linear susceptibility by Shivaram and collaborators.

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Thursday, December 16, 2021
3:30 PM
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" New Direct Electron Imaging Techniques for Quantum Materials"


Dr. Kayla Nguyen , University of Illinois Urbana-Champaign
[Host: Utpal Chatterjee]
ABSTRACT:

Electron microscopy is transforming the physical sciences. Aided by a new generation of direct imaging detectors, cryo-electron microscopy won the 2017 Nobel Prize in Chemistry for advancements in visualization of biomolecules.  To go beyond traditional electron microscopy, new detectors must also be developed for the diffraction imaging; here, the scattered electron beam encodes a wealth of information about the structure, chemistry, electrical, optical, and magnetic properties of matter. During my PhD, I co-invented the electron microscopy pixel array detector (EMPAD), a fast, highly efficient detector designed to capture the full scattered electron information. The EMPAD has been licensed to Thermo Fisher Scientific and sold around the world. In my talk, I will highlight how the EMPAD enables new characterization techniques for imaging topological magnetic and ferroelectric structures.  These approaches can be used to uncover polarization fields, orbital angular momentum and chirality of polar and magnetic textures. By developing new characterization methods in combination with theoretical predictions, new physics in emerging quantum materials can be revealed with electron microscopy at atomic resolution.

 

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Thursday, December 9, 2021
3:30 PM
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ABSTRACT:

: The perfectly linear temperature dependence of the resistivity observed as T0 in a variety of metals close to a quantum critical point is a major puzzle of condensed matter physics. In cuprates, this phenomenon is observed in the vicinity of the pseudogap critical point p*. Using high magnetic fields to suppress superconductivity, one can access the normal state properties down to T0 close to this critical point. I will present high-field magneto-transport measurements of two hole-doped cuprates, near their respective p*, supporting that T-linear resistivity as T0 is a generic property of cuprates, associated with a universal scattering rate. We measured the low-T resistivity of Bi2Sr2CaCu2O8+δ just above p* [1] and found that it exhibits a T-linear dependence, quantitatively similar to other very different cuprates. We also observed, using the Drude formula, that in various cuprates showing this low-T phenomenon the slope of this T-linear resistivity is given by a universal relation implying a specific scattering rate for charge carriers: 1/�� = αh/2πkBT (corresponding to what is called the Planckian limit [2]), where h is Planck’s constant, kB is the Boltzmann constant and α a constant of order unity. Finally, we directly measured the scattering rate in La1.6xNd0.4SrxCuO4, just above p* and in the low-T limit, using angle-dependent magneto-resistance measurements [4]: these experiments reveal an inelastic scattering rate which is isotropic and linear in temperature, and whose magnitude is consistent with Planckian dissipation.
[1] Legros et al., Nat. Phys. 15, 142 (2019)
[2] Zaanen, SciPost Phys. 6, 061 (2019)
[3] Grissonnanche et al., Nature 595, 667 (2021)

Condensed Matter
Thursday, December 2, 2021
3:30 PM
Physics Building, Room 204
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ABSTRACT:

We consider the entanglement entropies of energy eigenstates in quantum many-body systems. For the typical models that allow for a field-theoretical description of the long-range physics, we find that the entanglement entropy of (almost) all eigenstates is described by a single crossover function. The eigenstate thermalization hypothesis (ETH) implies that such crossover functions can be deduced from subsystem entropies of thermal ensembles and that they assume universal scaling forms in quantum-critical regimes. They describe the full crossover from the groundstate entanglement scaling for low energies and small subsystem size (area or log-area law) to the extensive volume-law regime for high energies or large subsystem size. For critical 1d systems, the scaling function follows from conformal field theory (CFT). We use it to also deduce the scaling function for Fermi liquids in d>1 dimensions. These analytical results are complemented by numerics for large non-interacting systems of fermions in d=1,2,3 and the harmonic lattice model (free scalar field theory) in d=1,2. Lastly, we demonstrate ETH for entanglement entropies and the validity of the scaling arguments in integrable and non-integrable interacting spin chains.

References: PRL 127, 040603 (2021); PRA 104, 022414 (2021); arXiv:2010.07265.
 

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Thursday, November 18, 2021
3:30 PM
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"Quantum information processing based on spins in semiconductor quantum dots"


Dr. Yinyu Liu , Harvard University
[Host: Utpal Chatterjee]
ABSTRACT:

The field of Quantum Information is of great excitement in both fundamental physics and industry. One promising platform for quantum computing is gate defined quantum dot in semiconductors. The greatest limiting factor currently is that delicate quantum states can lose their quantum nature due to interactions with their environment. Other open challenges are to develop methods to entangle quantum bits that are separated by significant distances and can be measured quickly with high fidelity.

Silicon-based materials are promising due to the long lifetimes of electrons’ quantum states, but also challenging due to the difficulty in fabrication and valley degeneracy. I will report a singlet-triplet qubit with a qubit gate that is assisted by the valley states. This work would potentially relax the  design and fabrication requirement for scaling. Moreover, this research field has achieved strong coupling between electron spins and photons in hybrid circuit-QED architecture. Quantum optics, long distance quantum entanglement and communication via photons are promised. To address that, I will present my project on indium arsenate (InAs) double quantum dots (DQD) that are embedded in circuit-QED architecture. We demonstrated the direct evidence of photon emission from a DQD in the microwave regime and further achieved stimulated emission in a similar system. By achieving stimulated emission from one DQD in these works, we invented a semiconductor single atom maser that can be tuned in situ.  I will demonstrate that a semiconductor based quantum dot is a promising platform for quantum information as well as for fundamental physics.

Condensed Matter
Thursday, November 11, 2021
3:30 PM
Physics Building, Room 204
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"Quantum spin Hall effect in monolayer WTe2"


Wenjin Zhao , Cornell University
[Host: Prof. Dima Pesin]
ABSTRACT:

WTe2 is an example of a two-dimensional semimetal. It shows incredibly diverse and intriguing behavior such as the quantum spin Hall effect (QSH), superconductivity, ferroelectricity, and excitonic insulator, providing a new platform for studying the interplay between topology and correlations. In this talk I will discuss the helical nature of the QSH edge state in monolayer WTe2 and the proximity effect of a magnet upon it. In the first part, I will describe how we explore the spin-momentum locking in the QSH edge state and determine the spin axis by studying the magnetic anisotropy. In the second part, I will discuss the magnetic coupling between a two-dimensional antiferromagnet, CrI3, and the QSH edge state.

 

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Wednesday, November 3, 2021
2:00 PM
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"Quantum photonics with color qubits"


Chaitali Joshi , Caltech
[Host: Prof. Utpal Chatterjee]
ABSTRACT:

Optical photons are excellent flying qubits for long-distance quantum networks due to negligible thermal noise and decoherence at room temperature. In this talk, I will discuss how frequency encoding can be combined with nonlinear optics and fiber and integrated photonic technologies to address challenges in scaling future photonic quantum networks. Frequency multiplexing has had a profound impact on classical telecommunication networks, creating low loss and inexpensive hardware that can be exploited for quantum applications. I will describe quantum photonic applications where frequency encoding provides a distinct advantage in terms of scaling losses and resource overhead compared to polarization, spatial or temporal mode encoding.

Coherent manipulation of light in the frequency domain at the single-photon level requires a strong, noise-free nonlinear process. I will discuss our implementation of four-wave mixing (FWM) in a commercial dispersion-shifted fiber to achieve quantum frequency conversion with near-unity efficiency and low noise. I will discuss how we used this process as an active "frequency switch" to realize a low-loss multiplexed single-photon source that can be scaled to the deterministic regime. Next, I will discuss how we used this process as a frequency beam-splitter to demonstrate two-photon Hong-Ou-Mandel type interference between entangled photons of different colors- a hallmark of quantum indistinguishability. Finally, I will discuss our realization of a FWM-based "time lens" for the generation and detection of single-photon waveforms with picosecond r​esolution.

Based on Joshi et al., Nat. Comm. 9, 847 (2018), Joshi et al. Phys. Rev. Lett. 124, 143601(2020)

 
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Thursday, October 28, 2021
3:30 PM
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"Triangular Gross-Pitaevskii breathers and Damski-Chandrasekhar shock waves"


Professor Maxim Olchanyi (Olshanii) , University of Massachusetts Boston
[Host: Prof. Israel Klich]
ABSTRACT:

The recently proposed map [arXiv:2011.01415] between the hydrodynamic equations governing the two-dimensional triangular cold-bosonic breathers [Phys. Rev. X 9, 021035 (2019)] and the high-density zero-temperature triangular free-fermionic clouds, both trapped harmonically, perfectly explains the former phenomenon but leaves uninterpreted the nature of the initial (t=0) singularity. This singularity is a density discontinuity that leads, in the bosonic case, to an infinite force at the cloud edge. The map itself becomes invalid at time t=T/4. Here, we first map -- using the scale invariance of the problem -- the trapped motion to an untrapped one. Then we show that in the new representation, the solution [arXiv:2011.01415] becomes, along a ray in the direction normal to one of the three edges of the initial cloud, a freely propagating one-dimensional shock wave of a class proposed by Damski in [Phys. Rev. A 69, 043610 (2004)]. There, for a broad class of initial conditions, the one-dimensional hydrodynamic equations can be mapped to the inviscid Burgers' equation, a nonlinear transport equation. More specifically, under the Damski map, the t=0 singularity of the original problem becomes, verbatim, the initial condition for the wave catastrophe solution found by Chandrasekhar in 1943 [Ballistic Research Laboratory Report No. 423 (1943)]. At t=T/8, our interpretation ceases to exist: at this instance, all three effectively one-dimensional shock waves emanating from each of the three sides of the initial triangle collide at the origin, and the 2D-1D correspondence between the solution of [arXiv:2011.01415] and the Damski-Chandrasekhar shock wave becomes invalid.

Condensed Matter
Thursday, October 14, 2021
3:30 PM
Physics Building, Room 204
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"Predicted Nearly Room Temperature Superconductivity in Binary Metal Hydride Systems"


Tianran Chen , NIST Center for Neutron Research
[Host: Prof. Seung-Hun Lee]
ABSTRACT:

Due to the low atomic mass and high electron-phonon coupling strength in hydrogen-rich materials, hydride compounds under extremely high pressures are most promising in the search of high-Tc superconductors. First-principles-based computational search has become extremely important not only in predicting new materials but also in guiding high-pressure experimental measurements. In this work, we have developed a super-efficient and fast method for searching high-T hydride superconductors. We introduce new "metrics" that are strongly correlated to strong electron-phonon coupling and T but it is much faster to calculate them. Using our new method, we have searched more than 100,000 binary hydride systems and discovered several new high-T superconductors. Among them, we report our prediction of high-temperature superconductivity at relatively low pressure in a novel binary metal hydride which may break the current record. A detailed mechanism of the superconductivity, phonons, and electron-phonon coupling, anharmonicity, as well as the abnormal T -pressure dependence, will be also discussed.

Condensed Matter
Thursday, September 30, 2021
3:30 PM
Physics Building, Room 204
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"Machine Learning for Material Properties and Design"


Aravind Krishnamoorthy , University of Southern California
[Host: Utpal Chatterjee]
ABSTRACT:

The accelerated discovery and design of new quantum materials requires atomic-level information about chemical reactions, phase transformations, mechanical deformations and other collective and emergent quantum phenomena. Several techniques have been developed recently that can learn the potential energy surface (PES) of complex materials. Machine Learning (ML) models, particularly deep neural networks, have proven capable of learning highly complex non-linear relationships between atomic structure and properties and theory and experiments. In this talk, I will describe two examples of ML-driven MD called neural-network quantum molecular dynamics (NNQMD) to tackle problems related to large systems and long trajectories that cannot be investigated by Quantum Molecular Dynamics (QMD).

First, we use NNQMD for quantitatively characterizing the intermediate range order, manifested as first sharp diffraction peak in GeSe2. In the second example, we compute the dielectric constant, ε0, and its temperature dependence for liquid water using fluctuations in macroscopic polarization using two coupled neural network models. The first network, NNQMD, learns the PES of liquid water from QMD training data. The second network, neural-network maximally localized Wannier functions, NNMLWF, is trained to predict dipole moments.

I will also briefly discuss applications of ML to discovery of new dielectric polymer materials with high breakdown strengths and to optimization of chemical vapor deposition synthesis of quantum materials.

VIDEO:
Joint Condensed Matter and Gravity Seminar
Thursday, September 2, 2021
3:30 PM
Physics Building, Room 204
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"Coulomb Universe in a Jellium Droplet"


Professor Genya Kolomeisky , University of Virginia - Department of Physics
[Host: Prof. Israel Klich]
ABSTRACT:

Analogy between the Coulomb law of interaction between charges and the Newton law of gravitational attraction between masses is familiar to every physics student.  In this talk I demonstrate that this analogy implies that a system of identical charges can evolve with time in a manner that parallels cosmological evolution of the physical Universe with hallmarks such as Hubble's law and Friedmann-type dynamics present.  The Coulomb and Newton laws are also dissimilar because the electrostatic force is many orders of magnitude larger than the gravitational force whose manifestations are only noticeable on astronomical scale.  On the other hand, analog cosmological evolutions driven by Coulomb interactions are predicted to be observable in laboratory experiments involving Coulomb explosions and electron density oscillations in conductors.

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Thursday, April 29, 2021
3:15 PM
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ABSTRACT:

The pressure variable opens the door towards the synthesis of materials with unique properties, e.g. superconductivity, hydrogen storage media, high-energy density and superhard materials. Under pressure elements that would not normally combine may form stable compounds or they may adopt novel stoichiometries. As a result, we cannot use our chemical intuition developed at 1 atm to predict phases that become stable when compressed.

To facilitate the prediction of the crystal structures of novel materials, without any experimental information, we have deve loped XtalOpt, an evolutionary algorithm for crystal structure prediction. XtalOpt has been applied to predict the structures of hydrides with unique compositions that become stable at pressures attainable in diamond anvil cells. In the ternary hydride system two different classes of superconductors composed of S and H atoms have been discovered - methane intercalated H3S perovskites with the CSH7 stoichiometry, and phases containing SH honeyco mb sheets. We also predict a superconducting RbB3Si3 phase in the bipartite sodalite structure that could be synthesized at mild pressures and quenched to 1 atm.

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Meeting ID: 952 5366 8001
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Thursday, April 22, 2021
3:30 PM
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"The anomalous thermal relaxations in linear chemical reactions"


Saikat Bera , University of Virginia - Department of Physics
[Host: Marija Vucelja]
ABSTRACT:

Thermal quenching is the process of rapidly cooling or heating a material. It has been practiced since ancient times to obtain desirable mechanical properties in materials, especially metals. The dynamics in play during quenching fall in the regime of non-equilibrium dynamics and is a subject of interest as most processes in nature happen out of equilibrium. A curious phenomenon during out of equilibrium processes is the so called Mpemba effect. The Mpemba effect is a phenomenon where a system prepared at a hot temperature (Thot) “overtakes” an identical system prepared at a warm temperature (Twarm) and cools down faster to be in equilibrium with a cold environment (Thot > Twarm > Tenvironment). My project involves studying the dynamics and behavior of linear chemical reaction networks during this kind of out of equilibrium process. Chemical reaction networks are a good model to study various biochemical processes, which are integral to the study of biochemical pathways and thus the functioning of cells. I am especially searching for the existence of a Mpemba like behavior in these kinds of systems and trying to characterize their behavior and dependence on the different parameters of the linear chemical reaction network. In this seminar I will be detailing on the methods used to study the out of equilibrium dynamics of linear chemical reaction networks and will be presenting the preliminary results which indicates the existence of Mpemba like behavior. This understanding will eventually lead to the optimization of chemical production for industrial application and characterization of biochemical pathways.

Special Condensed Matter Seminar

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Meeting ID: 260 917 9512
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Tuesday, April 20, 2021
3:30 PM
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"Gutzwiller Quantum Molecular Dynamics Simulation in Liquid"


Chen Cheng , University of Virginia - Department of Physics
[Host: Gia-Wei Chern]
ABSTRACT:

The Gutzwiller approximation is a method for strongly-correlated systems, it is the simplest theory that successfully captures the correlated induced metal-insulator transition, i.e. mott transition. Density function theory (DFT) is a very efficient method to deal with many-electron systems, thus currently quantum molecular dynamics (QMD) simulations are dominantly based on DFT, however DFT fails to describe many strong electron correlation phenomenon, for example the mott transition.

We proposed a new scheme of quantum molecular dynamics based on the Gutzwiller method, the Gutzwiller quantum molecular dynamics (GQMD). A liquid Hubbard model is studied by GQMD, two schemes of mott metal-insulator transition is found at different densities, based on which a phase diagram can be given to describe different states of the Hubbard liquid system. An effort to apply GQMD to real materials is also made on hydrogen system at high temperature and pressure conditions.

 

 

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Thursday, April 15, 2021
3:30 PM
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"Machine Learning Enable the Large Scale Kinetic Monte Carlo for Falicov-Kimball Model"


Sheng Zhang , University of Virginia - Department of Physics
[Host: Gia-Wei Chern]
ABSTRACT:

The Falicov-Kimball (FK) model was initially introduced as a statistical model for metal-insulator transition in correlated electron systems. It can be exactly solved by combining the classical Monte Carlo method for the lattice gas and exact diagonalization (ED) for the itinerant electrons. However, direct ED calculation, which is required in each time-step of dynamical simulations of the FK model, is very time-consuming. Here we apply the modern machine learning (ML) technique to enable the first-ever large-scale kinetic Monte Carlo (kMC) simulations of FK model. Using our neural-network model on a system of unprecedented 105 lattice sites, we uncover an intriguing hidden sub-lattice symmetry breaking in the phase separation dynamics of FK model.

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Thursday, April 8, 2021
2:30 PM
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ABSTRACT:

I present a new computational paradigm to simulate time and momentum resolved inelastic scattering spectroscopies in correlated systems. The conventional calculation of scattering cross sections relies on a treatment based on time-dependent perturbation theory, that provides formulation in terms of Green’s functions. In equilibrium, it boils down to evaluating a simple spectral function equivalent to Fermi’s golden rule, which can be solved efficiently by a number of numerical methods. However, away from equilibrium, the resulting expressions require a full knowledge of the excitation spectrum and eigenvectors to account for all the possible allowed transitions, a seemingly unsurmountable complication. Similar problems arise when the quantity of interest originates from higher order processes, such as in Auger, Raman, or resonant inelastic X-ray scattering (RIXS). To circumvent these hurdles, we introduce a time-dependent approach that does not require a full diagonalization of the Hamiltonian: we simulate the full scattering process, including the incident and outgoing particles (neutron, electron, photon) and the interaction terms with the sample, and we solve the time-dependent Schrödinger equation. The spectrum is recovered by measuring the momentum and energy lost by the scattered particles, akin an actual energy-loss experiment. The method can be used to study transient dynamics and spectral signatures of correlation-driven non-equilibrium processes, as I illustrate with several examples and experimental proposals using the time-dependent density matrix renormalization group method as a solver. Even in equilibrium, we find higher order contributions to the spectra that can potentially be detected by modern instruments.

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Meeting ID: 921 7069 3950
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Thursday, March 25, 2021
3:30 PM
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"Quantum Wakes and Measurement Induced Chirality"


Matthew Wampler , University of Virginia - Department of Physics
[Host: Israel Klich]
ABSTRACT:

We study the long term behavior of lattice fermions undergoing repeated particle detection, extraction, or injection interspersed with unitary evolution in two specific regimes.  First, we investigate the wake pattern formed behind a moving probe performing these operations.  These disturbances show dramatically different behavior where, notably, at half-filling the “measurement wake” vanishes and the “extraction wake” becomes temperature independent.   Second, in analogy with the edge modes found in topologically trivial systems when undergoing floquet driving, we provide a protocol of repeated local density measurements that induces edge modes in a topologically trivial system while the hamiltonian remains time independent.  In the limit of rapid measurements, the so-called Zeno limit, we connect this system to a novel stochastic dynamical system and discover an interesting double step structure in the charge transport in this regime.    

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Meeting ID: 953 0813 2506
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Thursday, March 11, 2021
3:30 PM
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"Ferrimagnetic materials for room temperature small skyrmions"


Wei Zhou , University of Virginia - Department of Physics
[Host: Joe Poon]
ABSTRACT:

The magnetic skyrmions are topologically protected spin configuration, which stabilized by Dzyaloshinskii-Moriya interaction (DMI). Due to skyrmions’ ability to be small, stable, and controllable by electric current [1], they have considerable potential for high-density data storage applications. It is theoretically predicted that ferrimagnetic materials prefer holding small skyrmions at room temperature (RT) [2,3]. 10-15nm ferrimagnetic CoGd heterostructures and 10-15nm ferrimagnetic Mn4N heterostructures were fabricated by magnetron sputtering for holding small skyrmions at RT. Magnetic force microscope images show skyrmions. A designed compound layer is capping on the top of the magnetic layer to adjust the interfacial DMI, thus tune the size of skyrmions. The micromagnetic simulation was performed to study the effect of DMI on the size of skyrmions Mn4N.

 

Reference:
[1] Fert, A., et al. Magnetic skyrmions: advances in physics and potential applications. Nat Rev Mater 2, 17031 (2017).
[2] Büttner, F., et al. Theory of isolated magnetic skyrmions: From fundamentals to room temperature applications. Sci Rep 8, 4464 (2018).
[3] C.T. Ma., et al. Robust Formation of Ultrasmall Room-Temperature Neél Skyrmions in Amorphous Ferrimagnets from Atomistic Simulations. Sci Rep 9, 9964 (2019).
 
 

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