Kinetic energy driven superconductivity and pseugogap phase in weakly doped antiferromagnets

TL;DR

This paper presents an effective Hamiltonian for weakly doped antiferromagnets, showing that kinetic energy lowering via spin bipolarons drives superconductivity and explains the pseudogap phase in underdoped cuprates.

Contribution

It introduces a new effective Hamiltonian for spin polarons and elucidates the kinetic energy-driven mechanism for superconductivity and pseudogap formation in weakly doped antiferromagnets.

Findings

Superconductivity arises from kinetic energy lowering due to spin bipolarons.

Superconducting order vanishes as doping decreases, approaching the Mott insulator.

Pseudogap forms due to suppression of low-energy excitations in underdoped regions.

Abstract

We derive an effective Hamiltonian for spin polarons forming in weakly doped antiferromagnets and demonstrate that the system becomes superconducting at finite doping. We argue that the driving mechanism which gives rise to superconductivity is lowering of the kinetic energy by formation of mobile antiferromagnetic spin bipolarons. That source of attraction between holes is by definition effective if the antiferromagnetic correlation length is longer than the radius of forming polarons. Notwithstanding that the attraction is strongest in the undoped system with long range order, the superconducting order parameter vanishes when the doping parameter decreases which should be attributed to emptying the spin polaron band and approaching the Mott insulator phase. Since the hypothetical normal phase of low density gas of fermions is unstable against formation of bound hole pairs the intensity of low energy excitations is suppressed and the pseudogap forms in the underdoped region.