Experimental Approach to the Mechanism of High-Tc Superconductivity

Abstract

One of the most fascinating problems in solid state physics is the mechanism of high-transition-temperature (high-Tc) superconductivity discovered in layered copper oxides. The knowledge of the electronic structure is a key step toward the theoretical understanding of the mechanism of high-Tc superconductivity. We determine the band structure of single crystal of Bi2Sr2CaCu2O8 system by angle-resolved resonant photoemission measurement with synchrotron radiation [1,2]. We give a direct evidence for the Fermi-liquid states with O-2p character at the Fermi level in section 2. The nuclear magnetic resonance (NMR) study is a powerful tool which allows us to differentiate the microscopic properties between the copper and oxygen sites in both normal and superconducting states. We performed NMR study of enriched-17O in Y-Ba-Cu-O system by the collaboration with Prof. K. Asayama’s group [presented in this symposium], and found BCS-like enhancement of the nuclear-spin-lattice relaxation rate (1/T1) just below Tc [3,4]. We present an evidence that the high-Tc superconductivity is of s-wave type with O-2p hole Cooper pairing, while the Cu-3d holes are nearly localized with antiferromagnetic spin-fluctuation in section 3. To clarify the high-Tc mechanism, we also report the oxygen isotope effect for Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems in section 4 [5,6].