Structural and phonon anomalies in the superconducting Bi₂Sr₂CaCu₂O_8+σ with varying doping level at high pressures

Here we examined the effect of the lattice compression on the crystal structure of the Bi₂Sr₂CaCu₂O_8+σ superconductor with nearly optimally doped and overdoped composition using X-ray diffraction technique. Our studies show that at high pressures (up to 30 GPa ) the doping level does not affect the crystal structure of this superconductor. Along with this, structural anomalies in ratio appear at a pressure that corresponds to that at which T_c begins to decrease. This fact indicates a close connection between the observed anomalies and superconductivity. We also studied the effect of doping and pressure on the T_c(P) and on the Raman active lattice modes of the Bi₂Sr₂CaCu₂O_8+σ superconductors. We find universal suppression of the T_c by the pressure starting from the critical pressure P_c in the range from 9 to 16 GPa, depending on the doping level of the Bi₂Sr₂CaCu₂O_8+σ samples. Concomitantly, we observe phonon anomalies around 10 to 20 GPa, which indicate possible pressure-induced charge redistribution in BiO layers. These newly detected anomalies may be related to the changes in the electronic structure which compete with the superconductivity.. Authors: Xin, Jie [Fudan Univ., Shanghai (China); Center for High Pressure Science and Technology Advanced Research, Shanghai (China)] (ORCID:000900002395151X); Zhang, Jian-Bo [Center for High Pressure Science and Technology Advanced Research, Shanghai (China)]; Gu, Gen-Da [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:0000000298863255); Gavriliuk, Alexander G. [Institute for Nuclear Research RAS, Moscow (Russian Federation); A. V. Shubnikov Institute of Crystallography, Moscow (Russian Federation); Immanuel Kant Baltic Federal University, Kaliningrad (Russian Federation)]; Lyubutin, Igor [A. V. Shubnikov Institute of Crystallography, Moscow (Russian Federation)]. DOE Contract: SC0012704. Subjects: 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY