Real-time dynamics of the photoinduced topological state in organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$ under continuous-wave and pulse excitations

TL;DR

This paper theoretically investigates the real-time dynamics of photoinduced topological phase transitions in an organic conductor, revealing how continuous-wave and pulse excitations induce Floquet topological states and transient band structures.

Contribution

It provides a detailed theoretical analysis of the dynamical formation of Floquet topological states in an organic conductor under optical excitations, using a tight-binding model and time-dependent Schrödinger equation.

Findings

Hall conductivity exhibits slow oscillations related to Floquet band structure.

Transient spectra show formation of Floquet bands and gap opening during pulses.

Oscillation frequency of Hall conductivity increases with time towards pulse peak.

Abstract

We theoretically study the real-time dynamics of the photoinduced topological phase transition to a nonequilibrium Floquet Chern insulator in an organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$, which was recently predicted using the Floquet theory. By using a tight-binding model of $\alpha$-(BEDT-TTF)$_2$I$_3$ that hosts a pair of tilted Dirac-cone bands at the Fermi level, we solve the time-dependent Schr\"odinger equation and obtained time evolutions of physical quantities for continuous-wave and pulse excitations with circularly polarized light. We demonstrate that, for the continuous-wave excitations, time profiles of the Chern number and the Hall conductivity show indications of the Floquet topological insulator. We argue that the Hall conductivity exhibits a slow oscillation with its frequency corresponding to a photoinduced direct gap determined by the Floquet band structure. With pulse excitations, transient excitation spectra are obtained, from which we infer the formation of Floquet bands and the gap opening at the Dirac point during the pulse irradiation. This dynamical gap formation is also manifested by the slow oscillation component of the Hall conductivity; that is, its frequency increases with time toward the pulse peak at which it nearly coincides with the photoinduced direct gap. The relevance of the results to experiments is also discussed.