Experimental Signatures of Spin Superfluid Ground State in Canted Antiferromagnet Cr2O3 via Nonlocal Spin Transport

TL;DR

This paper demonstrates the existence of a spin superfluid ground state in Cr2O3 thin films at low temperatures, showing long-distance spin propagation and field-dependent critical behavior, advancing quantum spin transport understanding.

Contribution

It provides the first experimental evidence of spin superfluidity in a canted antiferromagnet, confirming theoretical predictions and opening avenues for spin supercurrent device development.

Findings

Long-distance spin propagation (~20 micrometers) observed in Cr2O3.

Nonlocal spin signals saturate below ~5 K, indicating a superfluid ground state.

Critical temperature follows a two-thirds power law near the phase transition.

Abstract

Spin superfluid is a novel emerging quantum matter arising from the Bose-Einstein condensate (BEC) of spin-1 bosons. We demonstrate the spin superfluid ground state in canted antiferromagnetic Cr2O3 thin film at low temperatures via nonlocal spin transport. A large enhancement of the nonlocal spin signal is observed below ~ 20 K, and it saturates from ~ 5 K down to 2 K. We show that the spins can propagate over very long distances (~ 20 micro meters) in such spin superfluid ground state and the nonlocal spin signal decreases very slowly as the spacing increases with an inverse relationship, which is consistent with theoretical prediction. Furthermore, spin superfluidity has been investigated in the canted antiferromagnetic phase of the (11-20)-oriented Cr2O3 film, where the magnetic field dependence of the associated critical temperature follows a two-thirds power law near the critical point. The experimental demonstration of the spin superfluid ground state in canted antiferromagnet will be extremely important for the fundamental physics on the BEC of spin-1 bosons and paves the way for future spin supercurrent devices, such as spin-Josephson junctions.