PC-P-12
Phase diagram of Bi2Sr2CaCu2O8+δ revisited from material point of view
16:45-18:15 29/11/2023
*S.Nakagawa1,2, J. Kato2,3, T. Kashiwagi1, T. Nishio3, H. Nakao4, S. Ishida2, H Eisaki2
1. Graduate School of Pure & Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
2. Research Institute for Advanced Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
3. Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
4. Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
High-TCcuprate superconductors exhibit a complex electronic phase diagram in which various electronic states coexist or compete depending on the carrier doping level on the CuO2 layers [1]. In Bi2Sr2CaCu2O8+δ(Bi2212), it is known that the doping level can be tuned over a wide range from underdoped to overdoped by post-annealing and changing excess oxygen content δ. Meanwhile, the change in oxygen content is accompanied by the change in the crystal structure. In addition, the compositional non-stoichiometry (e.g. mixing of Bi and Sr) and chemical substitution (e.g. Pb substitution with Bi) influence doping levels as well as crystal structure. These issues complicate our understanding of the doping dependence of electronic states. For example, the non-stoichiometry of the cation composition lowers the optimum TC[2], and the c-axis lattice constant depends non-monotonically on the oxygen content [3]. Thus, we have attempted to understand the influence of the chemical compositions on TC in Bi2212 from the viewpoint of crystal structure.
In this study, several Bi2212 single crystals with different cation compositions were grown using the Floating Zone method. Each crystal was annealed to prepare samples with a wide range of oxygen content. TC of each sample was evaluated using a SQUID magnetometer (MPMS). In addition, the a-, b-, and c-axis lattice constants and in-plane modulation structure period of each sample were evaluated through high-precision synchrotron radiation X-ray diffraction (KEK BL-4C). We found that, in the over-doped region, the a- and c-axis lattice constants increase monotonically with decreasing oxygen content, but this trend changes after a certain doping level (δkink). The position of δkink is systematically different depending on the cation composition, suggesting that the oxygen at different sites decreases after a certain oxygen content. We discuss the possibility that this phenomenon is related to the occurrence of oxygen vacancies, which has been pointed out in STM [4].
[1] B. Keimer et al., Nature 518, 179 (2015).
[2] H. Eisaki et al., Physical Review B 69, 064512 (2004).
[3] T. Fujii et al., Physical Review B 66, 024507 (2002).
[4] I. Zeljkovic et al., Science 337, 320 (2012).
This work was supported by the JSPS KAKENHI (No. JP19H05823).
