Abstract
In the framework of an effective functional approach based on the k · p method, we study the combined effect of an interface potential and a thickness of a three-dimensional (3D) topological insulator (TI) thin film on the spin Hall conductivity in layered heterostructures comprising TI and normal insulator (NI) materials. We derive an effective two-dimensional (2D) Hamiltonian of a 3D TI thin film sandwiched between two NI slabs and define the applicability limits of approximations used. The energy gap and mass dispersion in the 2D Hamiltonian, originated from the hybridization between TI/NI interfacial bound electron states at the opposite boundaries of a TI film, are demonstrated to change sign with the TI film thickness and the interface potential strength. Finally, we argue that the spin Hall conductivity can efficiently be tuned varying the interface potential characteristics and TI film thickness.
Highlights
From the viewpoint of the application perspective of solid-state materials with unusual electron properties for spintronic devices, design and fabrication of semiconductor heterostructures comprising three-dimensional (3D) topological insulator (TI) thin films interfaced with normal insulator (NI) films is undoubtedly a promising way [1,2,3,4,5,6,7,8]
Within the framework of the NI/TI/NI trilayer model based on a continual scheme, we argue that characteristics of electron states in the TI film are controlled by the film thickness and TI/NI interface potential whose variation can lead to the modification of topological properties of the system
In the previous sections we argued that both the interfaces and the edges play an important role in spin transport properties of the NI/TI/NI trilayer
Summary
From the viewpoint of the application perspective of solid-state materials with unusual electron properties for spintronic devices, design and fabrication of semiconductor heterostructures comprising three-dimensional (3D) topological insulator (TI) thin films interfaced with normal insulator (NI) films is undoubtedly a promising way [1,2,3,4,5,6,7,8]. Within the framework of continual approach, the influence of the NI slabs on electron states in the sandwiched 3D TI spacer film is taken into consideration through the boundary conditions specified by the effective interface potential (IP), which respects time-reversal symmetry Such analytic scheme has been developed and successfully used in the previous investigations [37,38,39,40] to show how the changes in the IP could modify the in-gap bound states at the TI/NI interface. We reveal that the quantized bulk response and the edge states, which exemplify spin Hall conductivity in the TI/NI heterostructures, are quite sensitive to the confinement factors such as the film thickness and the conditions at its boundaries These facts clearly indicate the limits of the feasibility of the QSHE regime in real samples.
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