Shen, Y.; Li, Y.-D.; Wo, H.; Li, Y.; Shen, S.; Pan, B.; Wang, Q.; Walker, H.C.; Steffens, P.; Boehm, M.; Hao, Y.; Quintero-Castro, D.L.; Harriger, L.W.; Frontzek, M.D.; Hao, L.; Meng, S.; Zhang, Q.; Chen, G.; Zhao, J.: Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate. Nature 540 (2016), p. 559-562
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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.