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 (23)

• Interface induced high temperature superconductivity in single unit-cell FeSe films on SrTiO3
• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• Observation of pseudogap behavior in a strongly interacting Fermi gas
• BCS-BEC Crossover and the Unitary Fermi Gas
• Electric-field-induced superconductivity in electrochemically-etched ultrathin FeSe films on SrTiO3 and MgO
• Charge carrier localization induced by excess Fe in the Fe1+y(Te,Se) superconductor system
• Critical role of substrate in the high temperature superconductivity of single layer FeSe on Nb:BaTiO${}_3$
• Strong electron correlations in the normal state of FeSe0.42Te0.58
• Fermi surface topology and low-lying quasiparticle dynamics of parent Fe${}_{1+x}$Te/Se Superconductor by orbital-polarization resolved ARPES
• Fermi surface topology and low-lying quasiparticle structure of magnetically ordered Fe1+xTe
• Unusual band renormalization in the simplest iron based superconductor
• Modeling the Fermi arc in underdoped cuprates
• Shallow pockets and very strong coupling superconductivity in FeSe_xTe_1-x
• Giant superconducting fluctuations in the compensated semimetal FeSe at the BCS-BEC crossover
• Electronic structure of Fe1.04(Te0.66Se0.34)
• Dynamics and mechanism of oxygen annealing in Fe${}_{1+y}$Te${}_{0.6}$Se${}_{0.4}$ single crystal
• Superconductivity vs bound state formation in a two-band superconductor with small Fermi energy -- applications to Fe-pnictides/chalcogenides and doped SrTiO3
• 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
• Experimental Observation of Incoherent-Coherent Crossover and Orbital Dependent Band Renormalization in Iron Chalcogenide Superconductors
• Seebeck effect in Fe1+xTe1-ySey single crystals
• Can one determine the underlying Fermi surface in the superconducting state of strongly correlated superconductors?
• Precursor Pairing Correlations and Pseudogaps

Cited by in corpus (6)

• Time Reversal Symmetry Breaking in the Fe-Chalcogenide Superconductors
• Magic gap ratio for optimally robust fermionic condensation and its implications for high-Tc superconductivity
• Emergent vortex Majorana zero mode in iron-based superconductors
• Direct visualization of sign reversal s^+- superconducting gaps in FeTe0.55Se0.45
• Mechanism of screening or enhancing the pseudogap throughout the two-band Bardeen-Cooper-Schrieffer to Bose-Einstein condensate crossover
• FeTe${}_{0.55}$Se${}_{0.45}$ van der Waals Tunneling Devices