| The quantum spin liquid,as a new topological quantum state system,exhibits a general disordered state of electron spin even at absolute zero,which is different from that of magnetic materials at low temperature.Although the spins are disordered,there are long-range entanglement between them,so they can be used in quantum communication and quantum computation.In addition,it is believed that high temperature superconductivity evolved by doping.Therefore,the study of quantum spin liquids is also helpful to explore the mechanism of high-temperature superconductivity.At present,quantum spin liquid systems are theoretically considered as a damping system based on triangular lattice or Kagome lattice.In 2006,Professor Alexei Kitaev of the California University of Technology proposed a topological spin model with an effective 1/2 spin on a two-dimensional hexagonal honeycomb lattice named the Kitaev quantum spin model.Different from the quantum spin liquid caused by the geometrically magnetic frustration,the magnetic disorder in the Kitaev quantum spin liquid is caused by the quantum frustrated effect in the system.The interaction between the spins is called the Kitaev interaction and the model has topological order.A two-dimensional quantum system with arbitrary excitation can be used as a fault-tolerant quantum computation.It is of great significance to find this kind of material experimentally.It is particularly important to find the real two-dimensional quantum system material with pure Kitaev model.Recently,it has been found that Kitaev and other interactions exist in a-RuCl3 material.However,the ground state of the material is the zigzag magnetic order.Because the ordered moment of the zigzag magnetic order is very small,the spin liquid behavior can be observed under various external conditions if the magnetic order is suppressed.The paper includes five parts.The first part introduces the research background of quantum spin liquid and a-RuCl3,and briefly explains the quantum spin liquid and the research results in recent decades.Then,Kitaev put forward a spin model with a ground state of spin liquid,which can be solved accurately.Fortunately,recently,in a-RuCl3 with quasi-two-dimensional honeycomb lattice,it is found that it has Kitaev interaction term.Spin liquid is very likely to be observed under the condition of adding field,which has aroused great concern at home and abroad in recent years.The second part:the principle of nuclear magnetic resonance(NMR)experiment,the pulse sequence,the laboratory device:spectrometer,power amplifier,network analyzer,magnets,high pressure packs,etc.The working principle of 200 MHz as an example is briefly described.In the third part,combined with specific heat and magnetic susceptibility measurement,a-RuCl3 induces the excitation of spin-free liquid with no energy gap in high magnetic field of NMR,and we obtain the magnetic phase diagram.Then the phase diagram of low field magnetic order is obtained by dielectric constant,and the quantum critical point is effectively marked.The existence of magnetoelectric coupling is proved,and it is speculated that a-RuCl3 may be the type-? multiferroics.In the fourth part,the change of a-RuCl3 under pressure is measured by means of high pressure magnetization and high pressure nuclear magnetic resonance.It is found that a nonmonotonic change of TN with the pressure,significantly,an obvious phase separation phenomena before entering the high-pressure magnetic disordered phase.Part five:the summary of the paper.Although we have measured and analyzed a-RuCl3 in many aspects,we have obtained the spin-excited states without energy gap induced by magnetic field and the peculiar high-pressure disordered phase.However,there are still some controversies,such as whether there is an energy gap under high field.It is hoped that the researchers will make some more significant contributions to the future exploration of quantum spin liquids. |
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