Phase fluctuations in two-dimensional superconductors and pseudogap phenomenon

TL;DR

This paper investigates how phase fluctuations in two-dimensional superconductors cause spectral broadening and pseudogap formation, confirmed through theoretical analysis and quantum Monte Carlo simulations.

Contribution

It provides a quantitative analysis of phase fluctuation effects on the pseudogap in 2D superconductors using both perturbative methods and numerical simulations.

Findings

Phase fluctuations broaden the spectral weight near the BCS gap.

The pseudogap phenomenon is linked to the ratio of coherence length to pairing correlation length.

Results are validated on the attractive-U Hubbard model with quantum Monte Carlo.

Abstract

We study the phase fluctuations in the normal state of generic two-dimensional superconducting systems with s-wave pairing. The effect of phase fluctuations of the pairing fields can be dealt with perturbatively using disorder averaging, after we treat the local superconducting order parameter as a static disordered background. It is then confirmed that the phase fluctuations above the two-dimensional Berezinskii-Kosterlitz-Thouless transition lead to a significant broadening of the single-particle spectrum, giving birth to the pseudogap phenomenon. Quantitatively, the broadening of spectral weights near the BCS gap is characterized by the ratio of the superconducting coherence length and the spatial correlation length of the superconducting pairing order parameter. Our results are tested on the fermionic attractive-U Hubbard model on the square lattice, using the unbiased determinant quantum Monte Carlo method and stochastic analytic continuation.