Correlated BCS wavefunction approach to unconventional superconductors

TL;DR

This paper introduces a modified BCS wavefunction with specific correlations to better describe unconventional superconductors, revealing non-standard excitations and robustness against disorder, aligning with experimental observations.

Contribution

It presents a novel correlated wavefunction approach that captures key features of unconventional superconductors not explained by traditional BCS theory.

Findings

Low-energy excitations have multiple poles in Green's function.

Particle-hole asymmetry observed in spectra.

D-wave pairing state is robust against weak disorder.

Abstract

We propose a modified BCS wavefunction as the ground state of a correlated superconductor with the correlation specified between $k$ and $-k$ electrons in the reciprocal space. Owing to this correlation, low-energy excitations are not conventional BCS Bogoliubov quasiparticles. They display at least four poles in the Green's function and their particle-hole weights in the tunneling and photon-emission spectrum become asymmetric. The superfluid density or superfluid stiffness also deviates from the BCS predictions with finite paramagnetic terms inside the total diamagnetic response. Moreover, a $d$-wave correlated pairing state becomes robust against weak disorders. Hence, this state can explain many mysterious features observed in unconventional superconductors like cuprates.