Triangular lattice of rare-earth ions with interacting effective spin-1/2 local moments is an ideal platform to explore the physics of quantum spin liquids (QSLs) in the presence of strong spin-orbit coupling, crystal electric fields, and geometrical frustration. The Yb delafossites, NaYbCh2 (Ch=O, S, Se) with Yb ions forming a perfect triangular lattice, have been suggested to be candidates for QSLs. Previous thermodynamics, nuclear magnetic resonance, and muon spin rotation measurements on NaYbCh2 have supported the suggestion of the QSL ground states. The key signature of a QSL, the spin excitation continuum, arising from the spin quantum number fractionalization, has not been observed. Here we perform both elastic and inelastic neutron scattering measurements as well as detailed thermodynamic measurements on high-quality single-crystalline NaYbSe2 samples to confirm the absence of long-range magnetic order down to 40 mK, and further reveal a clear signature of magnetic excitation continuum extending from 0.1 to 2.5 meV. The comparison between the structure of the magnetic excitation spectra and the theoretical expectation from the spinon continuum suggests that the ground state of NaYbSe2 is a QSL with a spinon Fermi surface.
@article{arxiv.2004.06867,
title = {Spinon Fermi surface spin liquid in a triangular lattice antiferromagnet NaYbSe$_2$},
author = {Peng-Ling Dai and Gaoning Zhang and Yaofeng Xie and Chunruo Duan and Yonghao Gao and Zihao Zhu and Erxi Feng and Zhen Tao and Chien-Lung Huang and Huibo Cao and Andrey Podlesnyak and Garrett E. Granroth and David Voneshen and Shun Wang and Guotai Tan and Emilia Morosan and Xia Wang and Hai-Qing Lin and Lei Shu and Gang Chen and Yanfeng Guo and Xingye Lu and Pengcheng Dai},
journal= {arXiv preprint arXiv:2004.06867},
year = {2021}
}