Tuning across the BCS-BEC crossover in the multiband superconductor Fe _{1+ <i>y</i>} Se _<i>x</i> Te _{1− <i>x</i>} : An angle-resolved photoemission study

Abstract

from 0.16 to 0.50, where Δ is the superconducting (SC) gap. We use angle-resolved photoemission spectroscopy to measure the Fermi energy, the SC gap, and characteristic changes in the SC state electronic dispersion as the system evolves from a BCS to a BEC regime. Our results raise important questions about the crossover in multiband superconductors, which go beyond those addressed in the context of cold atoms.