Tuning across the BCS-BEC crossover in the multiband superconductor Fe
 
 1+
 y
 
 Se
 
 x
 
 Te
 
 1−
 x
 
 : An angle-resolved photoemission study

Rinott, Shahar; Chashka, K. B.; Ribak, Amit; Rienks, E. D. L.; Taleb‐Ibrahimi, A.; Fèvre, P. Le; Bertran, F.; Randeria, Mohit; Kanigel, Amit

doi:10.1126/sciadv.1602372

Cited by 110 publications

(84 citation statements)

References 37 publications

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“…It was found experimentally that the dimensionless measure of the pairing strength, i.e. the ratio of the energy gap and the Fermi energy ∆/E F = 0.16, 0.3 and 0.5, increases monotonically with decreasing arXiv:1907.13344v1 [cond-mat.supr-con] 31 Jul 2019 of the iron excess y, exhibiting a crossover from the BCS to the BEC regime 23 . The investigation of the vortex core by means of scanning tunneling microscopy (STM) shows the presence of Friedel-like oscillations, confirming the BCS-BEC crossover nature of FeSe and a peculiar missing of the pseudogap 24 .…”

Section: Introductionmentioning

confidence: 99%

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

et al. 2019

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We investigate Bardeen-Cooper-Schrieffer (BCS) − Bose-Einstein condensation (BEC) crossover in a two-band superfluid Fermi gas with an energy shift between the bands. When the intraband coupling in the cold (first) band is fixed as weak, we find that in the case of vanishing interband interaction and in the strong-coupling limit of the hot (second) band the system undergoes a transition to a single-component configuration with the full suppression of the first energy gap and with the full redistribution of particles between bands. For non-vanishing interband interaction we reveal the non-monotonic dependence of the energy gap in the first band vs intraband coupling in the second band with the presence of a hump. In the case of weak interband coupling the system shows a significant amplification of the intrapair correlation length of the condensate in the first band in the strong-coupling regime of the second band, which clearly indicates the coexistence of giant Cooper pairs and a bosonic condensate even for nonzero temperatures. This can lead to a non-monotonic temperature dependence of the second energy gap with a peak. Here predicted coexistence of the giant Cooper pairs and bosonic molecules can be verified by means of the visualization of vortex cores in the two-component atomic condensates as well as in some iron-based superconductors.PACS numbers:

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Section: Introductionmentioning

confidence: 99%

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

et al. 2019

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“…In a realistic scenario, presence of additional symmetry breaking terms, such as Rashba cou- pling, is expected to further stabilize the unusual mixed symmetry states reported here [43]. [44,45]. These predictions can also be tested using ultracold Fermions on optical lattices where the interaction strength can be tuned with the help of Feshbach resonances [46][47][48][49].…”

Section: (C)-(d)mentioning

confidence: 83%

Topological transitions in a model for proximity-induced superconductivity

2019

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Using a prototype model for proximity induced superconductivity on a bilayer square lattice, we show that interlayer tunneling can drive change in topology of the Bogoliubov quasiparticle bands. Starting with topologically trivial superconductors, transitions to a non-trivial px + ipy state and back to another trivial state are discovered. We characterize these phases in terms of edge-state spectra and Chern indices. We show that these transitions can also be controlled by experimentally viable control parameters, the bandwidth of the metallic layer and the gate potential. Insights from our results on a simple model for proximity induced superconductivity may open up a new route to discover topological superconductors.

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“…In fact, this crossover has been realized in ultracold Fermi atomic gases [17,18], and currently, various properties and fluctuation phenomena of this system have been investigated theoretically and experimentally [19][20][21]. Interestingly, recent experiments of FeSe multi-band superconductors also indicated that this electron system is in the BCS-BEC crossover regime [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

“…Considering a two band configuration, where a strongly interacting shallow band is coupled with a weakly interacting deep band through the pair-exchange couplings [46], we show the evolution of the critical temperature, momentum distribution functions, chemical potential, and occupation number densities in each band. This specific band configuration is physically motivated by FeSe superconductors, which are believed to locate in the BCS-BEC crossover regime with a strongly interacting shallow band [35] and for which the BCS-BEC crossover can be tuned by chemical doping [24]. Therefore, we systematically investigate thermodynamic quantities in the two band model by changing the interaction in the shallow band from weak to strong.…”

Section: Introductionmentioning

confidence: 99%

BCS-BEC Crossover and Pairing Fluctuations in a Two Band Superfluid/Superconductor: A T Matrix Approach

2020

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We investigate pairing fluctuation effects in a two band fermionic system, where a shallow band in the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover regime is coupled with a weakly interacting deep band. Within a diagrammatic T matrix approach, we report how thermodynamic quantities such as the critical temperature, chemical potential, and momentum distributions undergo the crossover from the BCS to BEC regime by tuning the intraband coupling in the shallow band. We also generalize the definition of Tan's contact to a two band system and report the two contacts for different pair-exchange couplings. The present results are compared with those obtained by the simpler Nozières-Schmitt-Rink approximation. We confirm a pronounced enhancement of the critical temperature due to the multiband configuration, as well as to the pair-exchange coupling.PACS numbers:

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

Abstract: A BCS-BEC crossover in a multiband superconductor has been observed experimentally using ARPES.

Cited by 110 publications

References 37 publications

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

Topological transitions in a model for proximity-induced superconductivity

BCS-BEC Crossover and Pairing Fluctuations in a Two Band Superfluid/Superconductor: A T Matrix Approach

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Tuning across the BCS-BEC crossover in the multiband superconductor Fe 1+ y Se x Te 1− x : An angle-resolved photoemission study

Abstract: A BCS-BEC crossover in a multiband superconductor has been observed experimentally using ARPES.

Cited by 110 publications

References 37 publications

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

Topological transitions in a model for proximity-induced superconductivity

BCS-BEC Crossover and Pairing Fluctuations in a Two Band Superfluid/Superconductor: A T Matrix Approach

Contact Info

Product

Resources

About

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