Correlation Between Superconducting Gap and Pseudogap in High-T C Cuprates

Abstract

One of most striking features of high-Tc cuprates consists of an eccentric relationship between Tc and the maximum gap value 2Δ0 at T≪Tc1 particularly, in the underdoped (UD) region; Tc decreases with hole-doping level p while 2Δ0 continues to increase with p, which is in sharp contrast to the BCS result.1-6) This issue seems to be closely related to the development or existence of a pseudo gap (PG) in the normal state. Therefore, to clarify the nature of the PG as well as the superconductivity is very important for understanding the mechanism of the superconductivity in high-Tc cuprates. The PG was first reported as a spin gap (SG) in low- energy spin excitation spectrum in NMR relaxation-time T 1 experiments on underdoped YBa2Cu3O6+ð (Y123).7,8) The SG has been confirmed in the neutron scattering and uniform magnetic susceptibility measurements.9,10)