Impact of high-frequency pumping on anomalous finite-size effects in three-dimensional topological insulators

Abstract

Lowering of the thickness of a thin-film three-dimensional topological insulator down to a few nanometers results in the gap opening in the spectrum of topologically protected two-dimensional surface states. This phenomenon, which is referred to as the anomalous finite-size effect, originates from hybridization between the states propagating along the opposite boundaries. In this work, we consider a bismuth-based topological insulator and show how the coupling to an intense high-frequency linearly polarized pumping can further be used to manipulate the value of a gap. We address this effect within recently proposed Brillouin-Wigner perturbation theory that allows us to map a time-dependent problem into a stationary one. Our analysis reveals that both the gap and the components of the group velocity of the surface states can be tuned in a controllable fashion by adjusting the intensity of the driving field within an experimentally accessible range and demonstrate the effect of light-induced band inversion in the spectrum of the surface states for high enough values of the pump.

Structure of surface electronic states in strained mercury telluride

“…Since the real part of both localization parameters, κ ± , must be positive, the surface states (12) exist only for ε g > 0 (tensile strain). Physically, this means that the existence of the surface states (12), first, arises from the BIA terms (α = 0) and, second, it strongly depends on the sequence order of their parent bulk states, ψ ±1/2 and ψ ±3/2 . To find the dispersion of the surface states (12) for small wave vectors k s , we have to project the total Hamiltonian (1) to the subspace spanned by these two states, {Ψ 1 , Ψ 2 }.…”

“…Physically, this means that the existence of the surface states (12), first, arises from the BIA terms (α = 0) and, second, it strongly depends on the sequence order of their parent bulk states, ψ ±1/2 and ψ ±3/2 . To find the dispersion of the surface states (12) for small wave vectors k s , we have to project the total Hamiltonian (1) to the subspace spanned by these two states, {Ψ 1 , Ψ 2 }. Keeping the terms linear in k s , we arrive at the effective Hamiltonian,…”

“…Namely, TIs are condensed matter systems which behave like an insulator in their 3D bulk but have 2D gapless conducting electronic states protected by the time-reversal symmetry at their boundaries 1 . Up to date, such topologically protected electronic states were intensively studied theoretically and experimentally in various condensed matter structures [2][3][4][5][6][7][8][9][10][11][12][13] , and their optical analogs were also revealed [14][15][16][17][18] .…”

Phase transitions in intrinsic magnetic topological insulator with high-frequency pumping

“…Based on the Floquet theory that allows one to map a time-dependent problem into a stationary one, it has been shown that a periodic perturbation can induce topological phase transitions in a topological trivial insulator [44][45][46][47][48][49][50][51][52][53][54][55][56][57]. Later the corresponding Floquet topological insulators have been observed by experiments [45,46].…”

“…Also, it has been shown that an intense high-frequency linearly polarized light can be used to manipulate the value of a gap in of a non-doped topological insulator thin film [56]. However, the linearly polarized light cannot include the contribution of 1/ω, so that they only estimated the terms proportional to 1/ω 2 [56], where ω is the frequency of the polarized light. Noteworthy, the circularly polarized light can include the contribution of 1/ω.…”