Spin sensitive transport in a spin liquid material: revealing a robustness of spin anisotropy

TL;DR

This study uses spin Hall magnetoresistance measurements to reveal robust in-plane spin anisotropy in a-RuCl_3, a candidate quantum spin liquid, across a wide magnetic field range, indicating persistent spin correlations.

Contribution

It demonstrates spin-sensitive transport measurements uncover persistent in-plane spin anisotropy in a-RuCl_3, providing new insights into its spin correlations and quantum spin liquid behavior.

Findings

Oscillations in resistivity as a function of magnetic field angle observed from 1.5 T to 18 T.

Spins in a-RuCl_3 are largely locked to an in-plane axis, indicating a continuous-symmetry-broken state.

Persistent spin correlations suggest a robust anisotropic spin state beyond magnetic ordering range.

Abstract

Alpha-phase (a-) RuCl_3 has emerged as a prime candidate for a quantum spin liquid (QSL) that promises exotic quasiparticles relevant for fault-tolerant quantum computation. Here, we report spin sensitive transport measurements to probe spin correlation in a-RuCl_3 using a proximal spin Hall metal platinum (Pt). Both transverse and longitudinal resistivities exhibit oscillations as function of the angle between an in-plane magnetic field and the current, akin to previously measured spin Hall magnetoresistance (SMR) in antiferromagnet/Pt heterostructures. The oscillations are observed from 1.5 T to 18 T, both within and beyond the magnetic field range where the antiferromagnetic order and QSL state are reported in a-RuCl_3. The SMR oscillations show that spins in a-RuCl3 are largely locked to an in-plane quantization axis transverse to the magnetic field, constituting a continuous-symmetry-broken state that does not necessarily represent a long-range order. This robust anisotropy of spin axis uncovers critical energy scales connected with reported QSL signatures in a-RuCl_3. Simulations suggest a predominantly antiferromagnetic correlation to moderately high magnetic-fields, that may support the SMR oscillations. The coupling of the spin states within a-RuCl_3 and Pt demonstrated in our experiment opens a transport route to exploring exotic spin phases and device functionalities of QSL materials.