title: Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate.
abstract: 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 states, 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 YbMgGaO4that 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 proposal of quantum spin liquids.
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Shen
authors.affiliation: School of Computer Science, Fudan University, Shanghai 200433, China.
authors.forename: Yao-Dong
authors.initials: YD
authors.lastname: Li
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Hongliang
authors.initials: H
authors.lastname: Wo
authors.affiliation: Department of Physics, Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China.
authors.forename: Yuesheng
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Shoudong
authors.initials: S
authors.lastname: Shen
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Bingying
authors.initials: B
authors.lastname: Pan
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Qisi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, STFC, Chilton, Didcot OX11 0QX, UK.
authors.forename: H C
authors.initials: HC
authors.lastname: Walker
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble Cedex 9, France.
authors.forename: P
authors.initials: P
authors.lastname: Steffens
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble Cedex 9, France.
authors.forename: M
authors.initials: M
authors.lastname: Boehm
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Yiqing
authors.initials: Y
authors.lastname: Hao
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany.
authors.forename: D L
authors.initials: DL
authors.lastname: Quintero-Castro
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: L W
authors.initials: LW
authors.lastname: Harriger
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Frontzek
authors.affiliation: Neutron Scattering Laboratory, China Institute of Atomic Energy, Beijing 102413, China.
authors.forename: Lijie
authors.initials: L
authors.lastname: Hao
authors.affiliation: Neutron Scattering Laboratory, China Institute of Atomic Energy, Beijing 102413, China.
authors.forename: Siqin
authors.initials: S
authors.lastname: Meng
authors.affiliation: Department of Physics, Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China.|Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Qingming
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.|Center for Field Theory and Particle Physics, Fudan University, Shanghai 200433, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao