Tuning across the BCS-BEC crossover in the multiband superconductor Fe<sub>1+<i>y</i></sub> Se <sub><i>x</i></sub> Te<sub>1-<i>x</i></sub> : An angle-resolved photoemission study.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 28439547.
- Also identified by DOI 10.1126/sciadv.1602372 and PMC identifier 5400444.
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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<sub>1+<i>y</i></sub> Se <sub><i>x</i></sub> Te<sub>1-<i>x</i></sub> , by tuning the Fermi energy ε<sub>F</sub> via chemical doping, which permits us to systematically change Δ/ε<sub>F</sub> 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.