Tuning across the BCS-BEC crossover in the multiband superconductor Fe${}_{1+y}$Se${}_x$Te${}_{1-x}$ : An angle-resolved photoemission study

Abstract

The crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose-Einstein condensation (BEC) is difficult to realize in quantum materials because, unlike in ultracold atoms, one cannot tune the pairing interaction. We realize the BCS-BEC crossover in a nearly compensated semimetal Fe${}_{1+y}$Se${}_x$Te${}_{1-x}$ by tuning the Fermi energy, ${\epsilon }_F$, via chemical doping, which permits us to systematically change $\Delta /{\epsilon }_F$ from 0.16 to 0.5 were $\Delta$ 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.

References in corpus (8)

• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• Observation of pseudogap behavior in a strongly interacting Fermi gas
• Fermi surface topology and low-lying quasiparticle dynamics of parent Fe${}_{1+x}$Te/Se Superconductor by orbital-polarization resolved ARPES
• Modeling the Fermi arc in underdoped cuprates
• Giant superconducting fluctuations in the compensated semimetal FeSe at the BCS-BEC crossover
• Dynamics and mechanism of oxygen annealing in Fe${}_{1+y}$Te${}_{0.6}$Se${}_{0.4}$ single crystal
• Polarization Measurements and the Pairing Gap in the Universal Regime
• Band-edge BCS-BEC crossover in a two-band superconductor: physical properties and detection parameters

Cited by in corpus (3)

• Magic gap ratio for optimally robust fermionic condensation and its implications for high-Tc superconductivity
• Emergent vortex Majorana zero mode in iron-based superconductors
• Mechanism of screening or enhancing the pseudogap throughout the two-band Bardeen-Cooper-Schrieffer to Bose-Einstein condensate crossover