Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor

TL;DR

This paper explores the excitation spectra and pseudogap phenomena in a two-band superconductor across the BCS-BEC crossover, revealing how the deep band conceals the pseudogap in the shallow band, with implications for iron-based superconductors.

Contribution

It provides a theoretical analysis of the pseudogap hiding mechanism in two-band systems using the many-body T-matrix approximation, applicable to FeSe superconductors.

Findings

Pseudogap in the shallow band is hidden by the deep band contribution.

Spectral functions show two distinct contributions from the bands.

Results align with recent STM experiments on FeSe.

Abstract

We investigate single-particle excitation properties in the normal state of a two-band superconductor or superfluid throughout the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein-condensation (BEC) crossover, within the many-body T-matrix approximation for multi-channel pairing fluctuations. We address the single-particle density of states and the spectral functions consisting of two contributions associated with a waekly interacting deep band and a strongly interacting shallow band, relevant for iron-based multiband superconductors and multicomponent fermionic superfluids. We show how the pseudogap state in the shallow band is hidden by the deep band contribution throughout the two-band BCS-BEC crossover. Our results could explain the missing pseudogap in recent scanning tunneling microscopy experiments in FeSe superconductors.