arXiv subjects

Aayushi Agrawal

Publications and source records attributed to Aayushi Agrawal.

5 recordsLinked to original sources

arXiv2026

Floquet spintronics: tuning the current-induced spin polarization of topological surface states with light

Topological surface states are a promising platform for spintronics due to spin-momentum locking. Spin-momentum locking can induce a net spin polarization in topological surface states via an electric current, a phenomenon known as the Edelstein effect. In this work, using Floquet theory, we show that the current-induced spin polarization of topological surface states can be tuned by illuminating them with light, thereby modifying their spin texture in momentum space. Specifically, the electric spin susceptibility of topological surface states can be controlled and even reversed by varying the electric-field strength of high-frequency, circularly polarized light.

cond-mat.mes-hall↗

arXiv2024

Quasi-Majorana modes in the $p$-wave Kitaev chains on a square lattice

The topological characteristics of the $p$-wave Kitaev chains on a square lattice with nearest-neighbor and next-nearest-neighbor inter-chains hopping and pairing are investigated. Besides gapless exact zero-energy modes, this model exhibits topological gapless phase hosting edge modes, which do not reside strictly at zero energy. However, these modes can be distinguished from the bulk states. These states are known as pseudo- or quasi-Majorana Modes (qMMs). The exploration of this system's bulk spectrum and Berry curvature reveals singularities and flux-carrying vortices within its Brillouin zone. These vortices indicate the presence of four-fold Dirac points arising from two-fold degenerate bands. Examining the Hamiltonian under a cylindrical geometry uncovers the edge properties, demonstrating the existence of topological edge modes. These modes are a direct topological consequence of the Dirac semimetal characteristics of the system. The system is analyzed under open boundary conditions to distinguish the multiple MZMs and qMMs. This analysis includes a study of the normalized site-dependent local density of states, which pinpoints the presence of localized edge states. Additionally, numerical evidence confirms the robustness of the edge modes against disorder perturbations. The emergence of topological edge states and Dirac points with zero Chern number indicates that this model is a weak topological superconductor.

cond-mat.other↗

arXiv2023

Laser induced Flqouet topological phases in a 2D weak topological insulator with unconventional nonlinear dispersion

Recently, we presented a two-dimensional (2D) model of a weak topological insulator formed by stacking an $N$ number of Su-Schrieffer-Heeger (SSH) chains \cite{Agrawal_2022-02}. We now study the influence of periodic driving on the topological properties of this system, which has all the fundamental symmetries, by shining it with circularly polarized light (CPL). The CPL is chosen because it breaks the time-reversal symmetry, which induces more exotic topological properties in the system. We investigate two different formations of the $N$ stacked SSH chains: all the SSH chains are topologically trivial in one formation and nontrivial in the other one. In contrast to the undriven or static case, both formations exhibit distinct topological behaviors. Here, we particularly derive the Floquet or the effective Hamiltonian using the replica method, which facilitates the study of high- and low-frequency regimes. We have discovered that this model exhibits laser-induced Floquet topological phases with higher Chern numbers. This system has nonlinear dispersion along both directions with additional $k_x-k_y$ coupling terms, which made the dispersion of this system {\it unconventional}. We closely study the role of this unconventional dispersion in the system at the low-energy limit and its response to periodic driving. The low-energy Hamiltonian also reveals a hierarchy in the gaps of the neighboring Floquet bands. Interestingly, though this model has nonlinear quasi-energy dispersion, it still shows some signatures of hierarchy, which was observed in the system with linear dispersion like graphene. Furthermore, we study the effect of linearly polarized light (LPL) on the topological properties of the system. In response to the LPL driving, the band-touching point either opens up or splits into two band-touching points.

cond-mat.mes-hall↗

arXiv2023

Cataloging topological phases of $N$-stacked Su-Schrieffer-Heeger chains by a systematic breaking of symmetries

Two-dimensional (2D) model of a weak topological insulator with $N$-stacked Su-Schrieffer-Heeger (SSH) chain is studied. This study starts with a basic model with all the fundamental symmetries (chiral, time-reversal, and particle-hole) preserved. Different topological phases are introduced in this model by systematically breaking the system's symmetries. The symmetries are broken by introducing different bonds (hopping terms) in the system. First, the chiral symmetry is broken by introducing hopping within each sub-lattice or intra-sub-lattice hopping, where the hopping strengths of the sub-lattices are equal in magnitudes but opposite in sign. Then, following Haldane, the time-reversal (TR) symmetry is broken by replacing the real intra-sub-lattice hopping strengths with imaginary numbers without changing the magnitudes. We find that breaking chiral and TR symmetries are essential for the weak topological insulator to be a Chern insulator. These models exhibit nontrivial topology with the Chern number $C = \pm 1$. The preservation of the particle-hole (PH) symmetry in the system facilitates an analytical calculation of $C$, which agrees with the numerically observed topological phase transition in the system. An interesting class of topologically nontrivial systems with $C=0$ is also observed, where the non-triviality is identified by quantized and fractional 2D Zak phase. Finally, the PH symmetry is broken in the system by introducing unequal amplitudes of intra-sub-lattice hopping strengths, while the equal intra-sub-lattice hopping strengths ensures the preservation of the inversion symmetry. We investigate the interplay of the PH and the inversion symmetries in the topological phase transition. A discussion on the possible experimental realizations of this model is also presented.

cond-mat.str-el↗

arXiv2022

Floquet topological phases with high Chern numbers in a periodically driven extended Su-Schrieffer-Heeger model

The high Chern number phases with the Chern number |C| > 1 are observed in this study of a periodically driven extended Su-Schrieffer-Heeger (E-SSH) model with a cyclic parameter. Besides the standard intra-dimer and the nearest-neighbor (NN) inter-dimer hopping of the SSH model, an additional next-nearest-neighbor (NNN) hopping is considered in the E-SSH model. The cyclic parameter, which plays the role of a synthetic dimension, is invoked as a modulation of the hopping strengths. A rigorous analysis of different phase diagrams has shown multiple Floquet topological phase transitions among the high Chern number phases. These phase transitions can be controlled by the strength and frequency of the periodic driving. Instead of applying perturbation theory, the whole analysis is done by Floquet replica technique. This gives a freedom to study high as well as low-frequency effects on the system by considering less or more number of photon sectors. This system can be experimentally realized through a pulse sequence scheme in the optical lattice setup.

cond-mat.mes-hall↗