$\mu$SR evidence for the U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO$_4$

TL;DR

This study provides muon spin relaxation evidence that YbMgGaO$_4$ hosts a gapless U(1) quantum spin liquid ground state, showing no magnetic order or spin freezing down to very low temperatures.

Contribution

First direct muon spin relaxation evidence confirming the U(1) quantum spin liquid state in a triangular antiferromagnet.

Findings

No static magnetic order or spin freezing down to 0.048 K

Temperature-independent relaxation rates indicating gapless excitations

Supports the U(1) quantum spin liquid ground state

Abstract

Muon spin relaxation and rotation ($\mu$SR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO$_4$ indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in zero field. Below 0.4 K, the $\mu^{+}$ spin relaxation rates, which are proportional to the dynamic correlation function of the Yb$^{3+}$ spins,exhibit temperature-independent plateaus. Same behavior is revealed by temperature-independent local susceptibilities extracted from the Knight shifts of the $\mu^{+}$ spin rotation frequencies under a transverse field of 20 Oe. All these $\mu$SR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO$_4$.