压力下碱金属铁硒基超导体中的现象与物理

在凝聚态物理研究中, 压力作为对物质状态调控的独立变量得到了广泛的应用. 压力对发现物质的新现象、新规律及对其形成机理的理解和对相关理论的验证起到了重要的作用, 尤其在超导电性的研究中取得了巨大的成功. 文章简要的介绍了通过利用压力手段对具有相分离结构的碱金属铁硒基超导体A_xFe_2-ySe₂ (A=K, Rb, Tl/Rb)开展的系列研究所取得的实验结果, 以及其他一些文献中报道的在此方面的主要实验与理论研究工作, 包括压力导致的超导再进入现象和其产生的量子临界机理、其特有的反铁磁绝缘体相在该类超导体实现超导电性中的作用、化学负压力对超导电性的影响、构成该类超导体的反铁磁序与其寄居的超晶格的关系等.

Phenomena and findings in pressurized alkaline iron selenide superconductors

In the frontiers of condensed matter physics, pressure is widely adopted as an independent control parameter for tuning states of matters and plays an important role in finding new phenomena and corresponding physics, as well as in testing the relevant theories. Remarkably, a great deal of success has been achieved in searching for new superconductors and uncovering the microphysics for known superconductors. In this brief review, we attempt to describe the progress in high pressure studies of alkaline selenide superconductors A_xFe_2-ySe₂ (A=K, Rb, Tl/Rb).#br#The high-pressure studies of Tl_0.6Rb_0.4Fe_1.67Se₂, K_0.8Fe_1.7Se₂ and K_0.8Fe_1.78Se₂ superconductors show that after the ambient-pressure superconducting phase is completely suppressed under about 9 GPa, the reemergence of a pressure-induced superconductivity with a maximum T_c of 48.7 K is observed at ～11 GPa, which is the highest T_c in this kind of superconductor. The systematic investigations on transport and structural properties for K_0.8Fe_ySe₂ (y=1.7 and 1.78) reveal that a pressure-induced quantum phase transition occurs at pressure between 9.2 GPa and 10.3 GPa, where the antiferromagnetic state with Fermi liquid behavior converts into the paramagnetic state with non-Fermi liquid behavior. Therefore, it is proposed that the observed reemergence of superconductivity at high pressure is probably driven by the quantum critical transition.#br#In addition, some intriguing puzzles on these superconductors and corresponding possible answers are also reviewed from the perspective of high-pressure studies, including the roles of the insulating magnetic phase in developing/stabilizing ambient-pressure and high-pressure superconducting phases and the significance of the pressure-induced antiferromagnetic fluctuation state for the emergency of superconductivity in the high-pressure superconducting phase.