Voltage-driven exchange resonance achieving 100\% mechanical efficiency

TL;DR

This paper introduces a voltage-driven exchange resonance mechanism in ferromagnet-topological insulator heterostructures that achieves near-perfect mechanical efficiency by utilizing adiabatic quantum motor principles and topological charge pumping.

Contribution

It proposes a novel voltage-induced torque mechanism for high-frequency magnetization dynamics with near-unity efficiency, surpassing limitations of current-driven magnetic resonances.

Findings

Achieves 100% mechanical efficiency in magnetic resonance.

Demonstrates high-frequency exchange mode resonance.

Shows topological charge pumping at resonance.

Abstract

Magnetic resonances driven by current-induced torques are crucial tools to study magnetic materials but are very limited in frequency and mechanical efficiency. We propose an alternative mechanism, voltage-induced torque, to realize high efficiency in generating high-frequency magnetization dynamics. When a ferromagnet-topological insulator-ferromagnet trilayer heterostructure is operated as an adiabatic quantum motor, voltage-induced torque arises from the adiabatic motion of gapped topological electrons on the two interfaces and act oppositely on the two ferromagnetic layers, which can excite the exchange mode where the two ferromagnetic layers precess with a $\pi$-phase difference. The exchange mode resonance, bearing a much higher frequency than the ferromagnetic resonance, is accompanied by topological charge pumping, leading to a sharp peak in electrical admittance at the resonance point. Because the output current is purely adiabatic while dissipative current vanishes identically, the proposed voltage-driven exchange resonance entails a remarkably high mechanical efficiency close to unity, which is impossible in any current-driven systems.