Quantum spin liquids (QSLs) are exotic states of matter characterized by emergent gauge structures and fractionalized elementary excitations. The recently discovered triangular lattice antiferromagnet YbMgGaO4 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 YbMgGaO4 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 Γ 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 YbMgGaO4.
@article{arxiv.1708.06655,
title = {Fractionalized excitations in the partially magnetized spin liquid candidate YbMgGaO4},
author = {Yao Shen and Yao-Dong Li and H. C. Walker and P. Steffens and M. Boehm and Xiaowen Zhang and Shoudong Shen and Hongliang Wo and Gang Chen and Jun Zhao},
journal= {arXiv preprint arXiv:1708.06655},
year = {2019}
}