Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H04: Nonequilibrium Dynamics in Topological Phases of MatterInvited

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Sponsoring Units: DCMP Chair: Jason Alicea, Caltech Room: LACC 151 
Tuesday, March 6, 2018 2:30PM  3:06PM 
H04.00001: Quantum quench dynamics in topological systems Invited Speaker: Smitha Vishveshwara Can quench dynamics involving the dynamic tuning of a parameter in a system, such as a magnetic field, act as a probe of topological phases? Can the existence of topological order lead to a different realm in nonequilibrium dynamics? In this talk, I will address these two questions in the context of two hallmarks of topological phases – ground state degeneracies and the presence of edge modes. In the instance of quenching across a critical point separating a topological and a trivial phase, I will argue that under certain conditions, ground state degeneracies result in a ‘topological blocking’ phenomena. In such a situation, topological constraints force the system to completely occupy the excited spectrum of the final state and to have zero overlap with the final ground state. I will then describe the effect of edge modes on quenches in the paradigm Majorana wire system whose ends are expected to carry Majorana fermionic bound modes. Here, parity switches associated with the bound modes drastically affect nonequilibrium quench dynamics. In these contexts, I will discuss possible influences of disorder on topologically constrained nonequilibrium dynamics. Finally, I will propose that quantum Hall systems can behave as gravitational analogs and will explore potential simulations of black hole dynamics in these systems. 
Tuesday, March 6, 2018 3:06PM  3:42PM 
H04.00002: Dynamics in topological phases with constrained Hilbert spaces Invited Speaker: Anushya Chandran Many topological phases of matter, including superconductors, fractional quantum Hall fluids and spin liquids, are described at low energies by gauge theories with constrained Hilbert spaces. In this talk, I will discuss the steady states of such systems under their own quantum dynamics. 
Tuesday, March 6, 2018 3:42PM  4:18PM 
H04.00003: Disentangling signatures of Floquet topological systems Invited Speaker: Tami PeregBarnea Floquet theory helps us find steady state solutions to the time dependent Schrodinger equation when the Hamiltonian is periodic in time. By defining the quasi energy spectrum and quasi energy states one can identify topological features like edge modes and nonzero topological invariants. In some cases, a system which is nontopological at equilibrium becomes topological when a timeperiodic perturbation is applied. In this work we take a close look at these nonequilibrium topological states which are induced by the periodic perturbation and characterize their response functions. We find that the splitting into side bands can be seen in transport and suppress the ability to carry current. For example, in a 2D Floquet topological insulator attached to metallic leads at equilibrium the measured conductivity is not quantized although the system exhibits edge modes. This is due to the fact that the edge modes are split into many side bands and the overlap with the lead states at a particular energy reflects the splitting. Nevertheless, the current is carried only by edge modes and is therefore robust against weak perturbations. For certain cases like equilibrium leads or a sudden turn on of the periodic perturbation it is possible to calculate the strength of each side band and predict the transport properties. Results for DC and AC transport in driven systems will be presented. 
Tuesday, March 6, 2018 4:18PM  4:54PM 
H04.00004: Driving Topology with Light Invited Speaker: Alessandra Lanzara Optical manipulation of materials properties far from equilibrium has been an emerging field over the past few years, allowing access to transient melting of existing phases and onset of new electronic orders. The prospect that topology can also be controlled and switched with light is offering a new promising way to design new topological properties of solids. Here I will present spectroscopic studies in the time and spin domains of a 3D topological insulator and a 2D semimetal. Our studies reveal how the surface states forms and coevolve through a topological phase transition in the 3D topological insulator and how the transition from a topological trivial to a non trivial state can be induced. We also discuss the effect of structural properties in stabilizing these phases. The effect of resonant and non resonant excitations for variable pump strength will be also discussed. 
Tuesday, March 6, 2018 4:54PM  5:30PM 
H04.00005: Topology and stability of anomalous Floquet insulators Invited Speaker: Mark Rudner The discrete (rather than continuous) timetranslation symmetry of periodicallydriven "Floquet systems" gives rise to new types of intrinsically dynamical topological phases, which have no analogues in equilibrium. In this talk I will first review the novel features of topology in periodicallydriven systems. I will then demonstrate the stability of the twodimensional Anomalous Floquet Insulator (AFI)  an interacting (periodicallydriven) nonequilibrium phase that exhibits nontrivial micromotion within a driving period [1,2,3], and delocalized (thermalizing) chiral states at its boundaries. The AFI bulk is stabilized against heating by disorderinduced manybody localization (MBL). Crucially, while MBL is generically expected at high driving frequencies, the AFI (and in fact all "anomalous" phases that may arise only in periodicallydriven systems) require the driving frequency to be comparable to intrinsic energy scales of the system. Nonetheless we find conditions where the AFI is stable to interactions. The analytical approach that we develop is general, and can be applied to investigate the stability of a wide variety of anomalous Floquet phases. Finally I will discuss the quantized observables that serve as topological order parameters of the AFI. 
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