Pseudogap phenomena in the superconducting phase of the cuprates

Abstract

The presence of a normal state spectral (pseudo) gap at the superconducting transition temperature in the underdoped cuprates has important implications for the associated superconducting phase. We argue that this normal state pseudogap derives from pairing fluctuations, which necessarily persist below Tc and which have important implications on the superconducting state. Our Greens function approach, based on the equation of motion method, can be viewed as a natural extension of BCS theory for sufficiently strong pairing interaction, suggested by the short coherence length of the cuprates. In addition to the usual fermionic excitations, there are also incoherent (but not pre-formed) pairs of finite center of mass momentum which must be self consistently incorporated in computing Tc and other superconducting properties, such as the superfluid density and the Josephson critical current. Finally, we discuss some of the experimental implications of our theory for the cuprates.