Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate
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 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 proposal of quantum spin liquids.
Nature