P05S

22BG004, 23BG012

BL-9A

Comprehensive Studies of the Electronic Structure for theDouble-layer high-Tc Superconductor Bi2Sr2CaCu2O8+δ
- Revisit of the Phase Diagram by ARPES
Y. Tsubotaa, Y. Miyaib, S. Kumarb,c, K. Tanakad, S. Ishidae, H. Eisakie,
S. Nakagawaf, T. Kashiwagif, M. Aritab, K. Shimada a,b, and S. Idetaa,ba Graduate School of Advanced Science and Engineering, Hiroshima Univ., Higashi-Hiroshima 739-0046, Japanb Hiroshima Synchrotron Radiation Center (HiSOR), Hiroshima Univ., Higashi-Hiroshima 739-0046, Japan, Agency for Science, Technology and Research (A*STAR),
Singapore 138632, Singapore
dUVSOR-Ⅲ Synchrotron, Institute for Molecular Science, Okazaki, Aichi 444-8585, JapaneNational Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8560, JapanfDivision of Materials Science, Tsukuba University, Tsukuba, Ibaraki 305-8577, Japan
cInstitute of Microelectronics (IME)

Keywords: high-Tc cuprate superconductors, ARPES, electronic structure, strongly correlated electron materials

It has been known that the cuprate superconductors show a high superconducting (SC) transition
temperature (Tc) and exotic physical properties. However, the SC mechanism of cuprates has been unclear
yet. In order to understand the mechanism of the microscopic origin of the high-Tc cuprate, various
theoretical and experimental studies have been done so far [1]. In high-Tc cuprate superconductors,
superconductivity occurs by hole doping into the CuO2 plane. The superconducting transition temperature
Tc as a function of hole concentration was reported as schematically shown in Fig. 1 [2]. For the hole-doped
cuprate superconductors, it has been widely believed that the phase diagram is universal, and the highest Tc
occurs at the hole concentration of ~0.16. However, recent angle-resolved photoemission spectroscopy(ARPES) experiments indicated that the empirical phase diagram may not be universal and shifted toward
the overdoped region [3-5].
In this study, we have performed ARPES measurements systematically to directly investigate theelectronic structure of the underdoped, optimally doped, and overdoped regions with three different
compositions of the double-layer cuprate, Bi2Sr2CaCu2O8+ (Bi2212). We have estimated the holeconcentration of each sample from the Fermi-surface area and compared them quantitatively. Fig. 1 shows
the Fermi surface of the optimally doped Bi2212 with Tc = 92 K and determined the Fermi momentum (reddots in Fig. 1) from the ARPES lineshape analyses.
In this poster presentation, we will show the results of the hole concentration estimated from the Fermi
surfaces in Bi2212 for each sample and are compared with the previous study to understand the relationshipbetween the hole concentration and Tc, namely, the new phase diagram. In this study, we found that the phase
diagram differs from the reported one [2]; the maximum Tc shifts toward the overdoped region. Furthermore,
we have measured the electronic structure in which the pseudogap closes and verified its consistency withrespect to the carrier concentration below and above Tc. Based on the present ARPES study, we will show
the new phase diagram in Bi2212 and discuss the results in comparison with other studies [6,7].

FIGURE 1. Schematic phase diagram reported from Ref. [2] (left). Fermi surfaces of Bi2212 observed by ARPES (right).
Red dots indicate the Fermi momentum estimated from the momentum-distribution curves near the Fermi level. White curves
are the Fermi surfaces fitted by tight-binding model. The bonding and antibonding bands are shown by the white curves,
respectively.

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