Neutron Spectroscopy Evidence for a Possible Magnetic-Field-Induced Gapless Quantum-Spin-Liquid Phase in a Kitaev Material α-RuCl₃

【摘要】 As one of the most promising Kitaev quantum-spin-liquid（QSL） candidates,α-RuCl₃ has received a great deal of attention.However,its ground state exhibits a long-range zigzag magnetic order,which defies the QSL phase.Nevertheless,the magnetic order is fragile and can be completely suppressed by applying an external magnetic field.Here,we explore the evolution of magnetic excitations of α-RuCl₃ under an in-plane magnetic field,by carrying out inelastic neutron scattering measurements on high-quality single crystals.Under zero field,there exist spin-wave excitations near the M point and a continuum near the Γ point,which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state,respectively.By increasing the magnetic field,the spin-wave excitations gradually give way to the continuous excitations.On the verge of the critical field μ₀ H_c=7.5 T,the former ones vanish and only the latter ones are left,indicating the emergence of a pure QSL state.By further increasing the field strength,the excitations near the Γ point become more intense.By following the gap evolution of the excitations near the Γ point,we are able to establish a phase diagram composed of three interesting phases,including a gapped zigzag order phase at low fields,possibly gapless QSL phase near μ₀ H_c,and gapped partially polarized phase at high fields.These results demonstrate that an in-plane magnetic field can drive α-RuCl₃ into a long-sought QSL state near the critical field.更多还原

【Abstract】 As one of the most promising Kitaev quantum-spin-liquid（QSL） candidates,α-RuCl₃ has received a great deal of attention.However,its ground state exhibits a long-range zigzag magnetic order,which defies the QSL phase.Nevertheless,the magnetic order is fragile and can be completely suppressed by applying an external magnetic field.Here,we explore the evolution of magnetic excitations of α-RuCl₃ under an in-plane magnetic field,by carrying out inelastic neutron scattering measurements on high-quality single crystals.Under zero field,there exist spin-wave excitations near the M point and a continuum near the Γ point,which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state,respectively.By increasing the magnetic field,the spin-wave excitations gradually give way to the continuous excitations.On the verge of the critical field μ₀ H_c=7.5 T,the former ones vanish and only the latter ones are left,indicating the emergence of a pure QSL state.By further increasing the field strength,the excitations near the Γ point become more intense.By following the gap evolution of the excitations near the Γ point,we are able to establish a phase diagram composed of three interesting phases,including a gapped zigzag order phase at low fields,possibly gapless QSL phase near μ₀ H_c,and gapped partially polarized phase at high fields.These results demonstrate that an in-plane magnetic field can drive α-RuCl₃ into a long-sought QSL state near the critical field.更多还原