Spin Gap and Superconductivity in the Interlayer Pair Tunneling Model

TL;DR

This paper presents an exact solution of a simple interlayer pair tunneling model, revealing novel fermionic excitations and properties consistent with underdoped cuprates, including spin gaps and unconventional superconductivity.

Contribution

It introduces an exactly solvable interlayer pair tunneling model that explains unusual metallic and superconducting properties of underdoped cuprates.

Findings

Normal state has gapped spin-1/2 excitations.

Existence of fermionic spin-zero and charge ±2e excitations.

Superconductivity arises from an intralayer interaction opening a charge gap.

Abstract

A simple interlayer pair tunneling is solved exactly. We find that in the normal state spin-1/2 particle and hole excitations are gapped. But the state is an unusual metal, characterized by novel fermionic spin zero and charge +2e and -2e excitations that exist about their own Fermi surfaces. The model is consistent with a number of properties of the underdoped cuprates. At finite temperature the Fermi surface appears partially gapped, and at high temperatures the spin gap disappears completely. Superconductivity is induced by an additional intralyer interaction which opens a gap in the charge-fermion spectrum. The symmetry of this charge gap (and hence that of the order parameter) is igenerally different from the symmetry of one-electron or - hole gap. The former can be a d wave, while the latter is more complex.