Strongly correlated bosons mediating Cooper pairing in high temperature superconductivity of cuprates

Abstract

Despite much theoretical study concerning high-temperature superconductivity of cuprates, its microscopic theory still remains an insufficient stage. Of unsolved problems, the most fundamental problem is to identify fermions forming Cooper pairs and the interaction between these fermions. Especially, how two fermions can be bound into the Cooper pairs remains one of the biggest questions in condensed matter physics. We considered here whether the so-called “glue” binding the fermions can exist or not, using d-p model adopted in our recently proposed theory emphasizing that the electronic state of the cuprates superconductors can be represented by the doping-dependent composite fermions. Applying two steps canonical transformation to d-p model Hamiltonian, we find the possibility that there is a new type of glue which bears a close analogy to the plasmon in electron gas. The glue is a boson (we call it strongly correlated boson) constructed with d and p fermions. It is shown that BCS-like gap equation containing the attractive interaction mediated by this boson leads to the appearance of d-wave superconductivity in cuprates.