Recently, the research team of academician Zhao Zhongxian from the Institute of Physics of the Chinese Academy of Sciences / Beijing National Laboratory for Condensed Matter Physics (Preparation) Superconductivity Laboratory Sun Liling and doctoral student Guo Jing and their collaborators, together with Academician Mao Heguang of the Geophysical Laboratory of the Carnegie Institution , Dr. Chen Xiaojia and other cooperation, made new progress in the research of new iron-based superconductors high voltage. The results of this study were published in the recent Physical Review Letters [PRL 108, 197001 (2012)].
Superconductivity is a macroscopic quantum phenomenon exhibited by materials at lower temperatures. By applying external pressure or a magnetic field, the superconducting temperature of the superconductor can be changed, and even the superconductivity of the superconductor can be completely suppressed or some non-superconducting substances appear superconducting. Qualitatively speaking, the microscopic mechanism that produces these physical phenomena is that the superconductivity of matter is determined by its crystal structure, charge, orbital and spin states and their interactions, and the influence of these factors on superconductivity can be achieved by Changes in external parameters, such as applied pressure, magnetic field, etc., can be adjusted. Among them, pressure is an effective control method. It is unique in that it can effectively control the electronic structure and crystal structure of the system and related cooperative phenomena without changing the chemical composition of the research system, thereby generating new physical phenomena, and at the same time can provide a revealing of its internal physical mechanism. Experimental evidence in the stress dimension.
Academician Zhao Zhongxian's research group and collaborators found that this material was between 9.2 -10.3 by high-pressure in-situ transport performance and synchrotron radiation X-ray diffraction measurement of the new iron-based chalcogenide superconductor K0.8FeySe2 (where y = 1.7, 1.78) GPa produced a transition from the behavior of metallic Fermi liquid to the behavior of non-Fermi liquid, accompanied by the transition from antiferromagnetic to paramagnetic magnetism, and the characteristic peaks of iron order absence disappeared. These experimental results show that this new iron-based superconductor has undergone a quantum phase transition within this pressure range.
It is generally believed that the quantum phase transition caused by pressure in a strongly correlated electronic system can lead to a quantum coherent state of the system. At a sufficiently low temperature, a system in this quantum coherent state will produce superconductivity, such as a heavy fermion superconductor And this phenomenon has been found in organic superconductors. According to the results of this experiment, it can be speculated that the second superconductor induced by pressure in this new iron-based superconductor discovered by the research team reported by Nature recently (Nature 483, 67–69, 1 March 2012) The phase transition (that is, the superconducting transition temperature of such superconductors gradually decreases with the increase of pressure until it disappears; and when the pressure is higher than 10 GPa, the system enters the second superconducting state) is caused by this quantum phase transition Driven.
The experimental samples for this study were provided by the research team of Chen Xiaolong, Institute of Physics. The synchrotron radiation X-ray diffraction experiment was completed on the Shanghai light source BL15U1 line station.
The above research work was supported by related projects of the National Natural Science Foundation of China, the Ministry of Science and Technology and the Chinese Academy of Sciences.
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