Abstract
We theoretically investigate possible photoinduced topological phase transitions in the organic salt $\alpha$-(BEDT-TTF)$_2$I$_3$, which possesses a pair of inclined massless Dirac-cone bands between the conduction and valence bands under uniaxial pressure. The Floquet analyses of a driven tight-binding model for this material reveal rich photoinduced variations of band structures, Chern numbers, and Hall conductivities under irradiation with elliptically polarized light. The obtained phase diagrams contain a variety of nonequilibrium steady phases, e.g., the Floquet Chern insulator, Floquet semimetal, and Floquet normal insulator phases. This work widens a scope of target materials for research on photoinduced topological phase transitions and contributes to development of research on the optical manipulations of electronic states in matters.
Highlights
Photoinduced phase transitions have attracted a great deal of research interest [1,2,3,4,5]
Emergence of quantum Hall effects in a tight-binding model on the honeycomb lattice irradiated with circularly polarized light was theoretically predicted using the Floquet theory [6, 8], in which the band structure attains topological nature similar to that described by the Haldane model [32]
We find that the Floquet normal insulator phase appears when ω 0.75 eV, but its area in the phase diagram gets smaller as the light frequency ω increases and eventually disappears for ω 0.75 eV
Summary
Photoinduced phase transitions have attracted a great deal of research interest [1,2,3,4,5]. The Floquet analyses of a driven tight-binding model for this material reveals that the irradiation with elliptically polarized light opens a gap at the Dirac points located on the Fermi level, and the system becomes a topological insulator This so-called Floquet Chern insulator phase as a photoinduced nonequilibrium steady phase is characterized by a quantized topological number [40, 41] and conducting chiral edge states [42]. As argued in our previous paper [27], one advantage of the usages of organic compounds is that an effective amplitude of light is an order of magnitude larger than graphene because of much larger lattice constants as discussed later, which enhances experimental feasibility of the predicted photoinduced topological phase transitions Another advantage of α-(BEDT-TTF)2I3 is that the bands near the Fermi level [i.e., four bands in Fig. 1(c)] relevant to the electronic properties of this material are well separated from bands above and below them.
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