Fractionalized excitations in the partially magnetized spin liquid candidate YbMgGaO4

TL;DR

This study uses neutron scattering to reveal fractionalized excitations and spinon Fermi surfaces in the partially magnetized quantum spin liquid candidate YbMgGaO4, supporting its exotic quantum state nature.

Contribution

It provides experimental evidence of fractionalized excitations and spinon Fermi surfaces in YbMgGaO4 under magnetic fields, advancing understanding of quantum spin liquids.

Findings

Dispersive spin excitation continuum observed

Spectral crossing at the Gamma point under magnetic field

Field-dependent redistribution of spectral weight

Abstract

Quantum spin liquids (QSLs) are exotic states of matter characterized by emergent gauge structures and fractionalized elementary excitations. The recently discovered triangular lattice antiferromagnet YbMgGaO$_4$ is a promising QSL candidate, and the nature of its ground state is still under debate. Here, we use neutron scattering to study the spin excitations in YbMgGaO$_4$ under various magnetic fields. Our data reveal a dispersive spin excitation continuum with clear upper and lower excitation edges under a weak magnetic field ($H=2.5$ T). Moreover, a spectral crossing emerges at the $\Gamma$ point at the Zeeman-split energy. The corresponding redistribution of the spectral weight and its field-dependent evolution are consistent with the theoretical prediction based on the inter-band and intra-band spinon particle-hole excitations associated with the Zeeman-split spinon bands, implying the presence of fractionalized excitations and spinon Fermi surfaces in the partially magnetized YbMgGaO$_4$.