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 T 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 μ0Hc=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 Г point become more intense.By following the gap evolution of the excitations near the Г 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 μ0Hc,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.

National Laboratory of Solid State Microstructures and Department of Physics,Nanjing University,Nanjing 210093,China;School of Physical Science and Technology and ShanghaiTech Laboratory for Topological Physics,ShanghaiTech University,Shanghai 200031,China;School of Science,Nanjing University of Posts and Telecommunications,Nanjing 210023,China;Department of Applied Physics,Nanjing University of Science and Technology,Nanjing 210094,China;Helmholtz-Zentrum Berlin für Materialien und Energie GmbH,Hahn-Meitner-Platz 1D-14109 Berlin,Germany;China Institute of Atomic Energy,Beijing 102413,China;School of Engineering and the Built Environment,Edinburgh Napier University,Edinburgh EH10 5DT,United Kingdom;National Synchrotron Radiation Research Center,Hsinchu 30077,China;Collaborative Innovation Center of Advanced Microstructures,Nanjing University,Nanjing 210093,China

[1]Xiaoxue Zhao;Kejing Ran;Jinghui Wang;Song Bao;Yanyan Shangguan;Zhentao Huang;Junbo Liao;Bo Zhang;Shufan Cheng;Hao Xu;Wei Wang;Zhao-Yang Dong;Siqin Meng;Zhilun Lu;Shin-ichiro Yano;Shun-Li Yu;Jian-Xin Li;Jinsheng Wen-.Neutron Spectroscopy Evidence for a Possible Magnetic-Field-Induced Gapless Quantum-Spin-Liquid Phase in a Kitaev Material α-RuCl3)[J].中国物理快报（英文版）,2022(05):146-154

Gapless,defies,0Hc

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