Adiabatic photo-steering theory in topological insulators

Abstract

Feasible external control of material properties is a crucial issue in condensed matter physics. A new approach to achieving this aim, named adiabatic photo-steering, is reviewed. The core principle of this scheme is that several material constants are effectively turned into externally tunable variables by irradiation of monochromatic laser light. Two-dimensional topological insulators are selected as the optimal systems that exhibit a prominent change in their properties following the application of this method. Two specific examples of photo-steered quantum phenomena, which reflect topological aspects of the electronic systems at hand, are presented. One is the integer quantum Hall effect described by the Haldane model, and the other is the quantum spin Hall effect described by the Kane–Mele model. The topological quantities associated with these phenomena are the conventional Chern number and spin Chern number, respectively. A recent interesting idea, time-reversal symmetry breaking via a temporary periodic external stimulation, is also discussed.

Topological non-Hermitian origin of surface Maxwell waves

“…The winding of this spectrum across the interface exactly corresponds to the number of surface electromagnetic modes which are zero-helicity TE or TM-polarized waves. Second, we connect the topology of the bulk system to the topology of the parameter ε,µ ( ) space; this is analogous to earlier works [24,25] in the condensed-matter context. For Maxwell waves, the parameter space is split into four simply connected quadrants excluding the ε = 0 and µ = 0 lines, where the helicity is illdefined.…”