Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Y19: Floquet Topological Systems |
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Sponsoring Units: DCMP Chair: Betul Pamuk, Cornell University Room: Room 211 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y19.00001: Topological Phenomena in the Floquet-Lattice of Electrical Circuits Alexander Stegmaier, Ching Hua Lee, Alexander Fritzsche, Ronny Thomale Floquet-topological states are conventionally studied in the context of quantum mechanics' Schrödinger equation, a first-order ordinary differential equation. However, recent research has shown that topological states are a fundamental aspect of all types of lattice-like wave systems, such as optical waveguides, coupled mechanical oscillators or electrical circuit lattices. Investigating periodically modulated electric circuit networks, we find that the rich structure of the differential equations governing them present fertile grounds for the discovery of novel kinds of Floquet-Topological phenomena. I will discuss how the differences between Quantum mechanics' Schrödinger equation and an electrical circuits' higher-order differential equations manifest in the Floquet description, and what this implies for the possibility of emerging topological effects. |
Friday, March 10, 2023 8:12AM - 8:24AM Author not Attending |
Y19.00002: Floquet higher order topological insulators through time-varying topolectric circuits Scott E Kenning, Penghao Zhu, Jiho Noh, Taylor L Hughes, Gaurav Bahl Higher order topological insulators (HOTIs) are n-dimensional materials that exhibit gapless protected states having dimensionality n-2 or lower. While practical realizations are limited to three spatial dimensions, Floquet systems having periodic driving can be used to introduce synthetic dimensions that enable the exploration of higher dimensional physics. In this work we describe a general approach to producing Floquet HOTIs using time-varying topolectric circuits. Our approach enables dynamically reconfigurable time protocols and on-demand TI phases within the same material. As an explicit example, we discuss the realization of a Floquet quadrupole HOTI with anomalous dynamical polarization. This 2D material exhibits 0D corner modes analogous to a non-driven quadrupole HOTI, and additionally exhibits a new set of topologically protected states originating from interactions in the synthetic dimension. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y19.00003: Real-space multifold degeneracy in graphene irradiated by twisted circularly polarized light Suman Aich, Babak Seradjeh We study monolayer graphene coherently driven by twisted light carrying orbital angular momentum and a radial vortex profile. Using Floquet theory, we characterize the real-space structure of quasienergies and Floquet modes. We obtain the effective real-space Floquet Hamiltonian and show it supports crossings of Floquet modes, associated with high-symmetry K and Γ points of graphene, at specific radial positions from the vortex center. This yields a ring of vortex bound states whose number is a topological invariant. These bound states form a multifold degenerate structure in real space that is purely dynamically generated and controlled by the frequency and intensity of twisted light. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y19.00004: Decoherence of edge states in two-dimensional Floquet systems with temporal noise Bhargava Balaganchi Anantha Ramu Two-dimensional periodically driven systems exhibit interesting topological features which cannot be achieved in static systems. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y19.00005: Dynamic melting and condensation of topological dislocation modes Sanjib Kumar Das, Bitan Roy Bulk dislocation lattice defects are instrumental to identify translationally active topological insulators (TATIs), featuring band inversion at a finite momentum (K_{inv}). They harbor robust gapless modes around the dislocation core, when the associated Burgers vector (b) satisfies K_{inv} · b = π (modulo 2π). From the time evolution of the appropriate density matrix, here we show that when a TATI via a ramp enters into a trivial or topological insulating phase, devoid of any gapless dislocation mode, at least weak signatures of the original defect modes survive for a long time. More intriguingly, as the system ramps into a TATI phase, signature of the dislocation mode dynamically builds up. Such evolutions of dislocation modes are more prominent for slow ramps. We exemplify these generic outcomes for two-dimensional time-reversal symmetry breaking insulators. Proposed dynamic responses at the core of dislocation lattice defects can be experimentally observed on quantum crystals, optical lattices and various metamaterials with time tunable band gap. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y19.00006: Tunable Floquet-Bloch manipulation of surface states in the antiferromagnetic topological insulator MnBi_{2}Te_{4} Nina Bielinski, Rajas Chari, Julian May-Mann, Soyeun Kim, Yujun Deng, Anuva Aishwarya, Chandra Shekhar, Makoto Hashimoto, Donghui Lu, Jiaqiang Yan, Claudia Felser, Vidya Madhavan, Zhixun Shen, Taylor Hughes, Fahad Mahmood The Floquet-Bloch manipulation of materials using the time-periodic potential of a laser pulse is a promising route to generate and coherently control new phases of matter. So far, experimental realization has been limited to the manipulation of time-reversal symmetric and non-interacting systems such as graphene and the surface states of a 3D topological insulator. In this work, we realize Floquet-Bloch manipulation of a time-reversal broken system: the putative antiferromagnetic topological insulator MnBi_{2}Te_{4}. Using time- and angle-resolved photoemission spectroscopy (tr-ARPES) with a mid-infrared pump, we generate Floquet-Bloch sidebands and demonstrate a gap opening at the Dirac point with circularly polarized light. Combined with Floquet theory calculations, our results uncover a rich, tunable Floquet phase diagram that uniquely arises in MnBi_{2}Te_{4} due to the intrinsically broken time-reversal symmetry and the coherent dressing of an unequal number of particle- and hole-like bands. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y19.00007: Dynamic metal at the grain boundary of Floquet topological insulators Daniel J Salib, Bitan Roy Driven quantum materials often feature emergent topology solely arising from the time periodic drive, otherwise absent in static crystals, among which the dynamic bulk-boundary correspondence encoded by nondissipative gapless modes residing near the Floquet zone center and/or boundaries are the most prominent ones. Here we show that such dynamic topological crystal can harbor topologically robust gapless matallic state along the grain boundary in its interior when the Floquet-Bloch band inversion occurs at a finite momentum (K_{inv}), such that the Burgers vector (b) of the constituting array of dislocations satisfies K_{inv}·b = π (modulo 2π). Such in-gap topological bulk metal, which can appear at the center and/or edge of the underlying periodic Floquet Brillouin zone, results from the hybridization among the localized modes bound to the core of individual dislocation. We exemplify these general outcomes by considering a paradigmatic representative of time-reversal symmetry breaking two-dimensional insulating system. Possible experimental setup underpinning such emergent driven topological metallic states in real materials are also discussed. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y19.00008: Versatile Floquet Weyl semimetal phases in an anisotropic Dirac system Shun Okumura, Aditi Mitra, Takashi Oka Topological electronic states induced by periodic external fields such as laser light have attracted much attention [1]. Recently, it has been theoretically predicted that the time-reversal symmetry is broken by irradiating the three-dimensional Dirac semimetal with a circularly polarized laser, and the Floquet-Weyl semimetal state (FWSM) appears due to the chiral gauge field [2]. While it is well known that conventional Weyl semimetals can show anomalous Hall effect originating from the Berry curvature between the two Weyl points with opposite chirality, the topological natures and transport properties in the FWSM have not been detailed in a periodically driven system. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y19.00009: Topological Edge Modes in a Floquet Hyperbolic System Ali Fahimniya, Hossein Dehghani, Yang-Zhi Chou, Huy Nguyen, Alicia Kollar, Alexey V Gorshkov Periodically driven (Floquet) systems can exhibit new topological properties absent in equilibrium systems. One example [1] is the existence of anomalous topological edge modes while the bulk bands have zero Chern numbers. In this work, we study a Floquet insulating system consisting of sites on a finite two-dimensional hyperbolic lattice that tessellates a finite portion of a negatively curved space. We show that in our Floquet system, while the bulk states have zero Chern numbers, there exists a chiral topological edge band with no analog in equilibrium topological insulators. Our study extends previous investigations [2, 3, 4] of topology in hyperbolic lattices. Due to the unique property of negatively curved spaces, a finite ratio of a hyperbolic lattice belongs to its boundary, even in the thermodynamic limit. As a result, the edge modes of a topological system on a hyperbolic lattice comprise a finite ratio of the total density of states. Unlike previous works, the topological edge modes in our system are achieved by a multi-step driving protocol without any need for complex hoppings, i.e., magnetic fluxes threaded through the lattice. Finally, we study the protection of the edge modes against disorder. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y19.00010: Strain Induced Curvature in a Photonic Floquet Topological Insulator Alexander Fritzsche, Julius Beck, Lavi K Upreti, Alexander Stegmaier, Matthias Heinrich, Ronny Thomale, Alexander Szameit The research on topological states of matter of the past few decades has mainly focused on Euclidean or flat lattice geometries. Only very recently, the topological phenomena in negatively curved or Hyperbolic lattices have attracted significant attention and Hyperbolic lattice tilings were studied especially in electronic circuits and circuit QED. In this talk, we present a different approach to Hyperbolic geometries which can be applied in optical systems such as photonic waveguides or fiber loop setups. By straining a topological Floquet- or time-periodically driven- graphene lattice, we simulate a pseudomagnetic field as well as negative Gaussian curvature. This allows us to move smoothly from Euclidean to Hyperbolic space and tune the curvature continuously, which is impossible by studying different Hyperbolic tilings. In this talk we explore the interplay between this curvature and the topology of the Floquet system and discuss phenomena unobserved in Euclidean lattice geometries. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y19.00011: Topological phase transitions at finite temperature Paolo Molignini, Nigel R Cooper The ground states of noninteracting fermions in one-dimension with chiral symmetry form a class of topological band insulators, described by a topological invariant that can be related to the Zak phase. Recently, a generalization of this quantity to mixed states - known as the ensemble geometric phase (EGP) - has emerged as a robust way to describe topology at non-zero temperature. By using this quantity, we explore the nature of topology allowed for dissipation beyond a Lindblad description, to allow for coupling to external baths at finite temperatures. We introduce two main aspects to the theory of mixed state topology. First, we discover topological phase transitions as a function of the temperature T, manifesting as changes in winding number of the EGP accumulated over a closed loop in parameter space. We characterize the nature of these transitions and reveal that the corresponding non-equilibrium steady state at the transition can exhibit a nontrivial structure - contrary to previous studies where it was found to be in a fully mixed state. Second, we demonstrate that the EGP itself becomes quantized when key symmetries are present, allowing it to be viewed as a topological marker which can undergo equilibrium topological transitions at non-zero temperatures. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y19.00012: Quantized Uhlmann phase and edge-state suppression of quantum transport in Lindblad dynamics Chih-Chun Chien, Yan He The Uhlmann phase is a generalization of the Berry phase from pure states to mixed states. Quantized Uhlmann phase has been found in many quantum systems at finite temperatures, revealing its potential to be a finite-temperature topological indicator. We show that the quantization of the Uhlmann phase may survive quantum jumps from system-reservoir couplings by using the Lindblad equation to simulate quantum dynamics of topological systems. The robustness of the Uhlmann phase offers hope for finite-temperature quantum computation utilizing the Uhlmann holonomy. By introducing a density or temperature difference through the reservoirs and monitoring the Lindblad quantum dynamics, we show that the Su-Schrieffer-Heeger model exhibits edge-state suppression of quantum transport. In contrast, the bandwidth of the Kitaev chain dominates its dynamics, leaving no observable topological signature in transport at the single-particle level. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y19.00013: low-energy effects of two dimensional Dirac semimetals with interactions. Jinjing Yi, Jedediah H Pixley, Shiwei Zhang, Zhiyu Xiao, Daniele Guerci, Elio J König We discuss the effects of interactions and incommensuration on the low-energy properties of two dimensional Dirac semimetals. We focus on charge neutrality and in a model that possesses a magic-angle (i.e. vanishing Dirac velocity) and study the evolution of the interaction induced magnetic transition in the presence of a magic-angle. The model is investigated analytically using perturbation theory and a mean field description as well as numerically using Hartree-Fock and an auxiliary field quantum Monte Carlo approach. |
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