Resilience of d-wave superconductivity to nearest-neighbor repulsion

TL;DR

This study demonstrates that d-wave superconductivity in the extended Hubbard model remains resilient to large nearest-neighbor repulsion V at strong coupling, due to a balance of competing effects in the underdoped regime.

Contribution

It reveals that strong-coupling d-wave pairing persists despite large V, challenging prior assumptions about Coulomb repulsion destroying superconductivity.

Findings

Pairing is preserved when V<U/2 at strong coupling.

V increases J, enhancing pairing at low frequency.

Pseudogap and Mott physics protect superconductivity from V.

Abstract

Many theoretical approaches find d-wave superconductivity in the prototypical one-band Hubbard model for high-temperature superconductors. At strong-coupling (U > W, where U is the on-site repulsion and W=8t the bandwidth) pairing is controlled by the exchange energy J=4t^2/U. One may then surmise, ignoring retardation effects, that near-neighbor Coulomb repulsion V will destroy superconductivity when it becomes larger than J, a condition that is easily satisfied in cuprates for example. Using Cellular Dynamical Mean-Field theory with an exact diagonalization solver for the extended Hubbard model, we show that pairing, at strong coupling, is preserved even when V>>J, as long as V<U/2. While at weak coupling V always reduces the spin fluctuations and hence d-wave pairing, at strong coupling, in the underdoped regime, the increase of J=4t^2/(U-V) caused by V increases binding at low frequency while the pair-breaking effect of V is pushed to high frequency. These two effects compensate in the underdoped regime, in the presence of a pseudogap. While the pseudogap competes with superconductivity, the proximity to the Mott transition that leads to the pseudogap, and retardation effects, protect d-wave superconductivity from V.