Nonlocal Magnetoresistance Mediated by Spin Superfluidity

TL;DR

This paper investigates how spin superfluidity in magnetic insulators mediates nonlocal magnetoresistance in metallic contacts, demonstrating that ac currents enable coherent spin transport despite magnetic anisotropy, with potential for magnetic system characterization.

Contribution

It introduces a method to detect and analyze spin superfluidity through nonlocal magnetoresistance and ac transport, providing new tools for magnetic system characterization.

Findings

Charge currents induce spin supercurrents in magnetic insulators.

AC currents enable coherent spin transport despite anisotropy.

Resonance peaks in ac transport reveal interfacial and dynamic properties.

Abstract

The electrical response of two diffusive metals is studied when they are linked by a magnetic insulator hosting a topologically stable (superfluid) spin current. We discuss how charge currents in the metals induce a spin supercurrent state, which in turn generates a magnetoresistance that depends on the topology of the electrical circuit. This magnetoresistance relies on phase coherence over the entire magnet and gives direct evidence for spin superfluidity. We show that driving the magnet with an ac current allows coherent spin transport even in the presence of U(1)-breaking magnetic anisotropy that can preclude dc superfluid transport. Spin transmission in the ac regime shows a series of resonance peaks as a function of frequency. The peak locations, heights, and widths can be used to extract static interfacial properties, e.g., the spin-mixing conductance and effective spin Hall angle, and to probe dynamic properties such as the spin-wave dispersion. Thus, ac transport may provide a simpler route to realizing nonequilbrium coherent spin transport and a useful way to characterize the magnetic system, serving as a precursor to the realization of dc superfluid spin transport.