High-pressure x-ray absorption and diffraction study of the self-doped superconductor EuFBiS2

E. Paris, B. Joseph, C. Marini, K. Terashima, T. Wakita, T. Yokoya, Y. Mizuguchi, T. Mizokawa, N. L. Saini
2020 Physical review B  
The BiS 2 -based layered materials are characterized by a highly susceptible physical state, revealing a large response to external conditions. A particular case is the EuFBiS 2 compound, showing a superconducting transition temperature T c ∼ 0.3 K at ambient pressure. Upon increasing external pressure, T c goes through a large amplification, accompanied by a structural phase transition (SPT) from tetragonal to monoclinic symmetry. Here, we use a combination of Eu L 3 -edge x-ray absorption
more » ... troscopy and synchrotron x-ray diffraction to unveil the evolution of the Eu valence and lattice symmetry under high pressure. We find that the average Eu valence increases gradually with pressure, exhibiting a pressure plateau near the SPT, at which the T c increases sharply. Since in EuFBiS 2 the charge carriers are introduced via self-doping induced by the mixed valence of the Eu ions, our findings clearly indicate that the role of the charge doping is marginal in the T c enhancement. On the other hand, the structural distortions, taking place at the SPT, play a central role in enhancing the superconducting properties of the EuFBiS 2 system.
doi:10.1103/physrevb.101.214526 fatcat:gewh6y5fwzclzl4m6y3lntenhm