Field-Tunable Topological Phase Transitions and Spin-Hall Effects in 2D Crystals

TL;DR

This paper demonstrates that silicene and related 2D crystals can undergo topological phase transitions controlled by an electric field, enabling tunable spin currents and potential applications in spintronics and quantum computing.

Contribution

It provides the first detailed analysis of electric field-induced topological phase transitions and spin-Hall effects in silicene-class 2D crystals, with implications for device applications.

Findings

Berry curvature can be tuned by electric field

Topological insulator to band insulator transition confirmed

Large, switchable spin currents observed

Abstract

As recent additions to the catalog of 2D crystals, silicene and other silicene-class crystals have numerous unique properties currently being investigated and considered for use in novel device applications. In this paper, we investigate electronic and transport properties of silicene in a field effect transistor geometry. We find that the Berry curvature of silicene-class crystals can be continuously tuned by a perpendicular electric field. By direct calculation of the $Z_2$ invariant, we confirm that an electronic phase transition from a topological insulator to a band insulator occurs when the electric field passes a critical value. In a device setting with asymmetric gate voltages, this field-tunable Berry curvature generates a large spin current transverse to the charge current. When the electric field strength surpasses the critical value, the bulk spin current is found to change direction and greatly decrease in magnitude. This finding of a large magnitude, switchable spin current suggests that the silicene family of 2D crystals could be an attractive candidate for field-tunable charge-spin conversion. Such field-tunable phase transitions between topologically distinct phases could be useful for robust qubits as well.