Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4

TL;DR

This study provides neutron-scattering evidence of a quantum spin liquid state in YbMgGaO4, revealing a magnetic excitation continuum at very low temperatures, driven by specific interactions on a triangular lattice.

Contribution

It demonstrates the presence of a QSL in YbMgGaO4 and identifies antiferromagnetic next-nearest-neighbor interactions as crucial for its formation.

Findings

Observation of a magnetic excitation continuum at 0.06 K

Identification of antiferromagnetic next-nearest-neighbor interactions

QSL state stabilized by planar anisotropy and specific interactions

Abstract

A quantum spin liquid (QSL) is an exotic state of matter in which electrons' spins are quantum entangled over long distances, but do not show symmetry-breaking magnetic order in the zero-temperature limit. The observation of QSL states is a central aim of experimental physics, because they host collective excitations that transcend our knowledge of quantum matter; however, examples in real materials are scarce. Here, we report neutron-scattering measurements on YbMgGaO4, a QSL candidate in which Yb3+ ions with effective spin-1/2 occupy a triangular lattice. Our measurements reveal a continuum of magnetic excitations - the essential experimental hallmark of a QSL - at very low temperature (0.06 K). The origin of this peculiar excitation spectrum is a crucial question, because isotropic nearest-neighbor interactions do not yield a QSL ground state on the triangular lattice. Using measurements of the magnetic excitations close to the field-polarized state, we identify antiferromagnetic next-nearest-neighbor interactions in the presence of planar anisotropy as key ingredients for QSL formation in YbMgGaO4.