Chiral d+is superconducting state in the two dimensional t-t' Hubbard model

TL;DR

This study uses a variational approach to the t-t' Hubbard model to reveal a quantum phase transition from d-wave to s-wave superconductivity, passing through a chiral d+is phase that breaks time reversal symmetry.

Contribution

It introduces a novel variational method to analyze superconducting phases in the t-t' Hubbard model, uncovering a new chiral d+is state with potential relevance to cuprate superconductors.

Findings

Identified a quantum phase transition between d-wave and s-wave superconductivity.

Discovered an intermediate chiral d+is phase with broken time reversal symmetry.

Suggests possible bulk time reversal symmetry breaking in overdoped cuprates.

Abstract

Applying the recently developed variational approach to Kohn-Luttinger superconductivity to the t-t' Hubbard model in two dimensions, we have found, for sizeable next-nearest neighbor hopping, an electron density controlled quantum phase transition between a d-wave superconducting state close to half filling and an s-wave superconductor at lower electron density. The transition occurs via an intermediate time reversal breaking d+is superconducting phase, which is characterized by nonvanishing chirality and density-current correlation. Our results suggest the possibility of a bulk time reversal symmetry breaking state in overdoped cuprates.