Microwave-driven ferromagnet--topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices

TL;DR

This paper explores heterostructures combining topological insulators and ferromagnetic insulators, demonstrating their potential as efficient spin batteries and quantized charge pumps driven by microwave-induced magnetization precession.

Contribution

It introduces a novel heterostructure design that enables pure spin current and quantized charge pumping, with robustness against disorder and geometric modifications.

Findings

Pure spin current can be pumped without bias voltage.

Quantized conductance ratios are achievable over a wide range of conditions.

Device robustness is maintained against weak disorder and geometric changes.

Abstract

We study heterostructures where a two-dimensional topological insulator (TI) is attached to two normal metal (NM) electrodes while an island of a ferromagnetic insulator (FI) with precessing magnetization covers a portion of its lateral edges to induce time-dependent exchange field underneath via the magnetic proximity effect. When the FI island covers both lateral edges, such device pumps pure spin current in the absence of any bias voltage, thereby acting as an efficient spin battery with giant output current even at very small microwave power input driving the precession. When only one lateral edge is covered by the FI island, both charge and spin current are pumped into the NM electrodes. We delineate conditions for the corresponding conductances (current-to-microwave-frequency ratio) to be quantized in a wide interval of precession cone angles, which is robust with respect to weak disorder and can be further extended by changes in device geometry.