Author: ["Yao Shen","Yao-Dong Li","Hongliang Wo","Yuesheng Li","Shoudong Shen","Bingying Pan","Qisi Wang","H. C. Walker","P. Steffens","M. Boehm","Yiqing Hao","D. L. Quintero-Castro","L. W. Harriger","M. D. Frontzek","Lijie Hao","Siqin Meng","Qingming Zhang","Gang Chen","Jun Zhao"]
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Abstract
A spin excitation continuum across a large region of the Brillouin zone that persists at near-zero temperatures provides evidence for a quantum spin liquid state with a spinon Fermi surface in YbMgGaO4. There are only a handful of candidate quantum spin liquids—exotic states of matter that are ideal for the study of the fundamental nature of quantum matter—so experimental observations of quantum spin liquid behaviour are scarce. Jun Zhao and colleagues use inelastic neutron scattering to study a single crystal of YbMgGaO4, which has a perfect triangular lattice. They find a spin excitation continuum across a large region of the Brillouin zone that persists at near-zero temperatures, providing evidence for a quantum spin liquid state with a spinon Fermi surface. The authors suggest that YbMgGaO4 fits the criteria for a perfect spin-1/2 triangular lattice antiferromagnet, as originally proposed by Philip Anderson in 1973. A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states1,2,3,4, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). Here we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO4 that reveal broad spin excitations covering a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle–hole excitation of a spinon Fermi surface. Our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO4, which has a perfect spin-1/2 triangular lattice as in the original proposal4 of quantum spin liquids.Cite this article
Shen, Y., Li, YD., Wo, H. et al. Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate. Nature 540, 559–562 (2016). https://doi.org/10.1038/nature20614 