Abstract
External driving is emerging as a promising tool for exploring new phases in quantum systems. The intrinsically nonequilibrium states that result, however, are challenging to describe and control. We study the steady states of a periodically driven one-dimensional electronic system, including the effects of radiative recombination, electron-phonon interactions, and the coupling to an external fermionic reservoir. Using a kinetic equation for the populations of the Floquet eigenstates, we show that the steady-state distribution can be controlled using the momentum and energy relaxation pathways provided by the coupling to phonon and Fermi reservoirs. In order to utilize the latter, we propose to couple the system and reservoir via an energy filter which suppresses photon-assisted tunneling. Importantly, coupling to these reservoirs yields a steady state resembling a band insulator in the Floquet basis. The system exhibits incompressible behavior, while hosting a small density of excitations. We discuss transport signatures and describe the regimes where insulating behavior is obtained. Our results give promise for realizing Floquet topological insulators.
- Received 26 February 2015
DOI:https://doi.org/10.1103/PhysRevX.5.041050
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Published by the American Physical Society
Popular Summary
Laser driving has recently been proposed as a tool to dynamically control the properties of materials, potentially unlocking new functionalities “on demand.” These proposals have raised significant interest, as well as many crucial questions about how a system’s delicate quantum properties can be controlled in the harsh world of real materials where electrons are awash in crystal vibrations and electromagnetic radiation. To realize the promise of such optically controlled topological phenomena, it is therefore essential to develop a clear understanding of the factors that govern the environment’s impact on a driven system and how these factors can be shaped to our advantage. Here, we explore dynamically altering the band topology of electronic systems using coherent irradiation.
We focus on a periodically driven, one-dimensional electronic system as a prototype to investigate the steady-state characteristics of Floquet topological insulators (i.e., driven systems that are internally insulating but may conduct along their surfaces). We provide an in-depth view into the dissipation mechanisms that determine the steady states of Floquet topological insulators, considering the inevitable coupling of such systems to phonons and the electromagnetic environment, as well as to external particle reservoirs. We identify means of “bath engineering” to ensure that heating by the drive is suppressed, and we find conditions under which the system flows to a steady state in which its nontrivial topology may hopefully be observed.
Our findings represent an important step forward in the theoretical description of so-called “Floquet topological insulators.” Future studies of the role of electron-electron interactions along with targeted searches for viable materials and experimental probes will be useful for realizing optical control of band topology in semiconductor systems.