# Evidence for a Field-induced Quantum Spin Liquid in $\alpha$-RuCl$_3$

## TL;DR

This study provides experimental evidence that $ ext{α}$-RuCl$_3$ exhibits a field-induced quantum spin liquid state characterized by a linear increase in spin gap with magnetic field, supporting theoretical predictions of a Kitaev QSL.

## Contribution

The paper presents direct NMR evidence of a magnetic field-induced quantum spin liquid in $ ext{α}$-RuCl$_3$, demonstrating a field-dependent spin gap incompatible with conventional magnetic order.

## Key findings

- Spin gap opens above 10 T magnetic field
- Spin gap increases linearly with field, reaching ~50 K at 15 T
- Spin gap is nearly isotropic with respect to field direction

## Abstract

We report a $^{35}$Cl nuclear magnetic resonance study in the honeycomb lattice, $\alpha$-RuCl$_3$, a material that has been suggested to potentially realize a Kitaev quantum spin liquid (QSL) ground state. Our results provide direct evidence that $\alpha$-RuCl$_3$ exhibits a magnetic field-induced QSL. For fields larger than $\sim 10$ T a spin-gap opens up while resonance lines remain sharp, evidencing that spins are quantum disordered and locally fluctuating. The spin gap increases linearly with increasing magnetic field, reaching $\sim50$ K at 15 T, and is nearly isotropic with respect to the field direction. The unusual rapid increase of the spin gap with increasing field and its isotropic nature are incompatible with conventional magnetic ordering and in particular exclude that the ground state is a fully polarized ferromagnet. The presence of such a field-induced, gapped QSL phase has indeed been predicted in the Kitaev model.