Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S54: Quenches and Transport in Driven Topological Systems 
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Sponsoring Units: DCMP Room: Mile High Ballroom 2A 
Thursday, March 5, 2020 11:15AM  11:27AM 
S54.00001: Quantized energy pumping in quasiperiodically driven Nitrogen Vacancy Centres Anushya Chandran, Ivar Martin, Philip Crowley A spin strongly driven by two incommensurate tones can exhibit a topological class of dynamics in which it (i) pumps energy from one drive to the other at a quantized average rate, in precise relationship with the quantum Hall effect, and (ii) exhibits an oscillatory response to a perturbation to the phases of the drives. We show these remarkable signatures to be realized in experiments in Nitrogen Vacancy centres. We further provide an experimental demonstration of halfinteger quantization of various responses at the transition between the topological and trivial classes of dynamics. 
Thursday, March 5, 2020 11:27AM  11:39AM 
S54.00002: Z2 topological quench dynamics PokMan Chiu, PoYao Chang In this talk, we present a quench setup for a realization of a Z2 topological quench dynamics in 3+1 dimensions. We show the Z2 feature can be identified from the flow of Berry phase. In addition, the entanglement spectra in both real and frequency space reveal the topological features. Finally, we discuss some possible realizations of our model. 
Thursday, March 5, 2020 11:39AM  11:51AM 
S54.00003: Photoinduced interfacial chiral modes in threefold topological semimetal Seikh Islam, Alexander Zyuzin We investigate the chiral electronic modes at the interface between two regions of a threefold 
Thursday, March 5, 2020 11:51AM  12:03PM 
S54.00004: Spacetime group symmetry and response functions
Congjun Wu
University of California, San Diego Congjun Wu Recently, spacetime group was proposed to describe the dynamic crystalline symmetries of a large class of dynamic systems beyond the Floquet system (Xu and Wu, Phys. Rev. Lett. 120, 096401 (2018)), including laserdriven solid crystals, dynamic photonic crystals, and optical lattices. We further study its consequences on physical observables on the response functions by applying the group theory representation analysis. This work will provide useful guidance for studying physical properties in timedependent systems. 
Thursday, March 5, 2020 12:03PM  12:15PM 
S54.00005: Electrons in NarrowBand Moire Graphene: Electric and Magnetic TwoDimensional Bloch Oscillations Zhiyu Dong, Ali Fahimniya, Leonid Levitov Bloch oscillating electrons, moving in a twodimensional crystal under a DC electric field, are described, in a quasiclassical picture, by trajectories that wind quasiperiodically around the 2D Brillouin zone. The oscillations feature two or more discrete frequencies that depend on the field, but not on individual particle velocities, producing narrow lines in ensembleaveraged noise power spectrum. An externally applied magnetic field alters the dynamics, creating new types of Bloch oscillations that do not exist in onedimensional solids. The conventional “electric” oscillations persist at weak B fields; above a critical B value a different dynamics sets in that combines Bloch oscillations and Larmor drift. In this “magnetic” regime particle trajectories are extended in position space and confined in momentum space, with a complex chaotic behavior arising at the transition. 
Thursday, March 5, 2020 12:15PM  12:27PM 
S54.00006: Energy filtered leads for quantized transport in Floquet systems Netanel Lindner, Mads Kruse, Mark Rudner

Thursday, March 5, 2020 12:27PM  12:39PM 
S54.00007: Photoinduced Topological Phase Transition and Optical Conductivity of Black Phosphorene yousung kang, Kyungsun Moon We theoretically study the photoinduced topological phase transition of black phosphorene induced by laser light with moderateintensity, which can satisfy the experimentally realistic requirement to preserve the quality of the sample. By deriving the effective Floquet Hamiltonian in terms of pseudospin S=1/2 degrees of freedom, we calculate the Chern number and the optical conductivity of the system with varying laser frequency. As one can expect from the photonassisted transport, the longitudinal optical conductivity has a threshold frequency at Ω=△/h with △ being the band gap of black phosphorene. Unlike the longitudinal optical conductivity, the optical Hall conductivity sharply increases when hΩ goes beyond one half of the band gap △/2. We also show that the Chern number changes from trivial to nontrivial one upon increasing frequency beyond hΩ=△/2. 
Thursday, March 5, 2020 12:39PM  12:51PM 
S54.00008: Enhancement of High Harmonics Generation by Floquet Engineering Abhishek Kumar, Yantao Li, Babak H Seradjeh High hramonic generation (HHG) in gaseous systems and solids is well studied. Since periodically driven systems can produce harmonic response, it is important to study the influence of external driving on the HHG power spectrum. We formulate a theory of highharmonic current using Floquet theory of periodically driven systems. As an application of our theory, we study HHG in the SuSchriefferHeeger (SSH) model with and without periodic drive. We find that there is a significant enhancement in higher harmonincs when the system is driven. Moreover, this enhancement peaks for an optimal harmonic at a value that increases when the intensity of the laser is reduced. This means HHG can be generated even at lower pulse intensities in a Floquet system. We obtain analytical expressions for HHG power spectrum in the highfrequency approximation for driven SSH model. Further, we study the effects of laser polarization and occupation of Floquet bands on HHG in two dimensional systems. We also investigate the consequences of spatiotemporal symmetries and Floquet topology for HHG in Floquet systems. 
Thursday, March 5, 2020 12:51PM  1:03PM 
S54.00009: CorrelationEnhanced Quantized Charge Pumping Jacob Marks, Michael Schüler, Jan Budich, Thomas Devereaux We investigate charge pumping in the vicinity of orderobstructed topological phases. To explore this, we study a prototypical SuSchreifferHeefer model with nonlocal interaction that gives rise to orbital charge density wave order, and characterize the impact of this order on the model’s topological properties. In the ordered phase, where the manybody topological invariant loses quantization, we find that not only is quantized chage pumping possible, it is assisted by the collective nature of the orbital charge density wave order. 
Thursday, March 5, 2020 1:03PM  1:15PM 
S54.00010: Stability of dynamical quantum phase transitions in quenched topological insulators: From multiband to disordered systems Christian Mendl, Jan Budich Dynamical quantum phase transitions (DQPTs) represent a counterpart in nonequilibrium quantum time evolution of thermal phase transitions at equilibrium, where real time becomes analogous to a control parameter such as temperature. In quenched quantum systems, recently the occurrence of DQPTs has been demonstrated to be intimately connected to changes of topological properties. Here, we contribute to broadening the systematic understanding of this relation between topology and DQPTs to multiorbital and disordered systems. Specifically, we provide a detailed ergodicity analysis to derive criteria for DQPTs in all spatial dimensions, and construct basic counterexamples to the occurrence of DQPTs in multiband topological insulator models. As a numerical case study illustrating our results, we report on microscopic simulations of the quench dynamics in the HarperHofstadter model. Furthermore, going gradually from multiband to disordered systems, we approach random disorder by increasing the (super) unit cell within which random perturbations are switched on adiabatically. This leads to an intriguing order of limits problem which we address by extensive numerical calculations on quenched onedimensional topological insulators and superconductors with disorder. (arXiv:1909.01402) 
Thursday, March 5, 2020 1:15PM  1:27PM 
S54.00011: Observation of long excitation lifetime in photoexcited Sbdoped Bi_{2}Se_{3 }nanoplatelets Adam Gross, Yasen Hou, Antonio Rossi, Dong Yu, Inna Vishik Bi_{2}Se_{3} is a threedimensional topological insulator (TI), characterized by a bulk band gap of approximately 0.3 eV and a Diraclike protected surface state. The material is usually ntype due to selenium vacancies, and chemical substitution, such as Sbdoping, is typically needed to bring the chemical potential into the bulk band gap. We will present ultrafast transient reflectivity measurements on Bi_{2}Se_{3} and Bi_{2x}Sb_{x}Se_{3} nanoplatelets which reveal starkly different carrier decay dynamics in ntype vs. insulating samples. This will be discussed in the context of optoelectronic applications of TIs, including as a material for exciton condensation. 
Thursday, March 5, 2020 1:27PM  1:39PM 
S54.00012: Timedomain anyon interferometry in Kitaev honeycomb spin liquids and beyond Kai Klocke, David Aasen, Roger Mong, Eugene Demler, Jason F. Alicea Motivated by recent evidence of a nonAbelian spin liquid in αRuCl_{3}, we introduce a new experimental method for probing the edge and quasiparticle content of such a phase. Our scheme exploits a pair of ancillary quantum spins that communicate via judicious timedependent tunneling of energy into and out of the spin liquid’s gapless chiral Majorana edge state. We show that the ancillaryspin dynamics not only probes the Majorana edge modes, but in suitable geometries allows one to detect individual nonAbelian anyons and emergent fermions via a timedomain counterpart of anyon interferometry developed in the quantumHall context. The tools that we develop are expected to be widely applicable to topological phases both in solidstate and coldatoms settings. 
Thursday, March 5, 2020 1:39PM  1:51PM 
S54.00013: Electron localization in twodimensional topological and nontopological bands Akshay Krishna, Matteo Ippoliti, Ravindra Nautam Bhatt Manybody localization (MBL) is a wellestablished phase present in disordered onedimensional spin models with shortrange interaction. However, the stability of MBL in higher dimensions, in the presence of long range interaction and under the effect of a topologically nontrivial singleparticle band structure, is still an area of ongoing research. We demonstrate a method to construct nearly flat subbands with arbitrary Chern numbers, using a weak periodic potential in the lowest Landau level. This twodimensional system is a novel platform for the detailed study of the interplay between disorder, interaction and topology in a continuum model. Using exact diagonalization, we investigate the localization properties of singleparticle eigenstates, as well as the tendency to manybody localize in the presence of interaction, both in the quasi 1D and 2D limits. Our results are based on an analysis of both the manybody eigenvalue spacings and the time evolution of an initial charge imbalance [1], [2]. 
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