Tunable spin-polarized edge transport in inverted quantum-well junctions

TL;DR

This paper explores how edge states in inverted HgTe/CdTe quantum wells can produce tunable, fully spin-polarized currents in double junction setups, even under small magnetic fields, using theoretical modeling and numerical simulations.

Contribution

It demonstrates the controllable spin-polarized edge transport in quantum well junctions, revealing spin-dependent oscillations and robustness of edge states under broken time-reversal symmetry.

Findings

Edge states carry spin-polarized currents under small magnetic fields.

Conductance exhibits spin-dependent Fabry-Perot oscillations.

Tunable, fully spin-polarized currents can be achieved via gate voltage.

Abstract

Inverted HgTe/CdTe quantum wells have been used as a platform for the realization of 2D topological insulators, bulk insulator materials with spin-helical metallic edges states protected by time-reversal symmetry. This work investigates the spectrum and the charge transport in HgTe/CdTe quantum well junctions both in the topological regime and in the absence of time-reversal symmetry. We model the system using the BHZ effective Hamiltonian and compute the transport properties using recursive Green's functions with a finite differences' method. Specifically, we have studied the material's spatially-resolved conductance in a set-up with a gated central region, forming monopolar (n-n$^{\prime}$-n) and heteropolar (n-p-n, n-TI-n) double junctions, which have been recently realized in experiments. We find regimes in which the edge states carry spin-polarized currents in the central region even in the presence of a small magnetic field, which breaks TRS. More interestingly, the conductance displays spin-dependent, Fabry-Per\'ot-like oscillations as a function of the central gate voltage producing tunable, fully spin-polarized currents through the device.