Quantum fluctuations, pseudogap, and the T=0 superfluid density in strongly correlated d-wave superconductors

TL;DR

This paper investigates how Coulomb interactions influence the superfluid density and pseudogap phenomena in strongly correlated d-wave superconductors at zero temperature, highlighting the role of electron correlations without competing orders.

Contribution

It develops a theoretical framework for phase fluctuations in a d-wave superconductor considering Coulomb interactions within the t-J-U model, revealing the doping dependence of phase stiffness.

Findings

Phase stiffness peaks at optimal doping and vanishes at half filling for large U.

Pseudogap phenomena can arise purely from electron correlations, without competing orders.

Superfluid density behavior aligns qualitatively with experimental observations in cuprates.

Abstract

I study the effect of Coulomb interaction on superconducting order in a d-wave lattice superconductor at T=0 by considering the superconducting saddle point in the two dimensional t-J-U model with an on-site repulsion U. The theory of low energy phase fluctuations around this saddle point is derived in terms of the effective hard-core bosons (representing the density of spin-up electrons and the order parameter phase), interacting with the fluctuating density of spin-down electrons. Whereas the saddle point value of the gap is found to monotonically increase towards half filling, the phase stiffness at T=0 has a maximum, and then decreases with further underdoping. Right at half filling the stiffness vanishes for large U. This argues that the pseudogap phenomenon of the type observed in cuprates is in principle possible without a development of any competing order, purely as a result of growing correlations in the superconducting state. The effects of finite temperature and disorder are discussed qualitatively.