Quantum Vortex Core and Missing Pseudogap in the Multiband BCS-BEC Crossover Superconductor FeSe

Hanaguri, T.; Kasahara, S.; Böker, J.; Eremin, I.; Shibauchi, T.; Matsuda, Yuji

doi:10.1103/physrevlett.122.077001

Cited by 73 publications

(66 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…For increasing hot-band coupling, we reveal a strong amplification of the critical temperature in comparison with the single-band case, with the interband coupling assisting such amplification, but not being crucial for its occurrence. In addition, in the intermediate (crossover) region between the BCS and BEC limits, the comparison between the critical temperature and the pair-breaking temperature shows a sig- nificant shrinking of the preformed-pair region, implying a possible reduction of the pseudogap effects, in lines with recent experimental findings for the FeSe multiband superconductors 57 . Finally, in the BEC regime with finite interband coupling, an interesting coherently coupled binary mixture of composite bosons is found.…”

supporting

confidence: 87%

Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC crossover in a two-band Fermi gas

et al. 2019

View full text Add to dashboard Cite

We study the superfluid critical temperature in a two-band attractive Fermi system with strong pairing fluctuations associated with both interband and intraband couplings. We focus specifically on a configuration where the intraband coupling is varied from weak to strong in a shallow band coupled to a weakly-interacting deeper band. The whole crossover from the Bardeen-Cooper-Schrieffer (BCS) condensation of largely overlapping Cooper pairs to the Bose-Einstein condensation (BEC) of tightly bound molecules is covered by our analysis, which is based on the extension of the Nozières-Schmitt-Rink (NSR) approach to a two-band system. In comparison with the single-band case, we find a strong enhancement of the critical temperature, a significant reduction of the preformed pair region where pseudogap effects are expected, and the entanglement of two kinds of composite bosons in the strong-coupling BEC regime.

show abstract

supporting

confidence: 87%

Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC crossover in a two-band Fermi gas

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Remarkably, the suppression is very effective, almost complete, even when the inter-band coupling is so small that the superconducting temperature is fully determined by the shallow band. Our results provide a solid explanation of the recent striking observation that the pseudogap was not detected in the multi-band BCS-BEC-crossover superconductor FeSe, which was called by the authors "a unique feature that is absent in a single band system" [46]. Notice that superconductivity is the most robust phase with respect to other instabilities that can arise when shallow bands and high density of states are present in the system.…”

supporting

confidence: 65%

Screening of pair fluctuations in superconductors with coupled shallow and deep bands: A route to higher-temperature superconductivity

et al. 2019

View full text Add to dashboard Cite

A combination of strong Cooper pairing and weak superconducting fluctuations is crucial to achieve and stabilize high-Tc superconductivity. We demonstrate that a coexistence of a shallow carrier band with strong pairing and a deep band with weak pairing, together with the Josephson-like pair transfer between the bands to couple the two condensates, realizes an optimal multicomponent superconductivity regime: it preserves strong pairing to generate large gaps and a very high critical temperature but screens the detrimental superconducting fluctuations, thereby suppressing the pseudogap state. Surprisingly, we find that the screening is very efficient even when the inter-band coupling is very small. Thus, a multi-band superconductor with a coherent mixture of condensates in the BCS regime (deep band) and in the BCS-BEC crossover regime (shallow band) offers a promising route to higher critical temperatures.PACS numbers: 74.20. De, 74.70.Ad Multi-band and multi-gap superconductors have demonstrated a potential to exhibit novel coherent quantum phenomena that can enhance the pairing energy and the critical temperature T c [1]. The well-known examples are magnesium diboride [2-4] and iron-based superconductors [5,6], where multiple Fermi surfaces can be effectively controlled by doping or by applying pressure [7,8]. Multi-band superconductivity can be also achieved in artificial inhomogeneous structures made of a single-band superconducting material -nanofilms, nanostripes or samples with spatially controlled impurity distributions [9][10][11][12].The phenomenon entangled with the multi-band superconductivity, important in this work, is the BCS-BEC crossover [13][14][15][16]. Proximity to this crossover in multiband materials with deep and shallow bands can give rise to a notable increase of superconducting gaps [17][18][19][20], which on the mean-field level leads to higher T c . The physical reason is the depletion of the Fermi motion in a shallow band, which yields short-sized pairs. In such materials the superconducting state is a coherent mixture of a BCS condensate in deep bands and BCS-BEC-crossover or even nearly BEC condensate in shallow bands. This takes place in, e.g., in MgB 2 [19], many of iron-based superconductors [8,[21][22][23][24] and in nanoscale samples [17,18].However, the largest enemy of the high-T c superconductivity in such materials is superconducting fluctuations. They are significant for the same reason which leads to a higher T c -the depletion of the carrier motion in a shallow band that is associated with a low super-conducting stiffness. The fluctuations give rise to the pseudogap state in the interval T c < T < T c0 , where the extracted from the mean-field calculations T c0 marks the appearance of incoherent and short lived Cooper pairs. The latter develop a coherent state below T cthe true critical temperature of the superconducting condensate [25,26]. For shallow bands T c ≪ T c0 and this eliminates all gains of the BCS-BEC crossover regime.In this Letter we consider the mechanis...

show abstract

“…Since pairing fluctuations are known to lower generally the superconducting/superfluid critical temperature, this screening effect is expected to enhance the critical temperature compared to the single band counterpart. Indeed, a missing pseudogap in the multi-band FeSe superconductors in the BCS-BEC crossover has been reported in a recent experiment [28]. Since single particle spectra in a single band system in the BCS-BEC crossover regime exhibit the pseudogap originating from strong pairing fluctuations [29][30][31][32], this experimental finding supports the screening of pairing fluctuations due to the multi-band nature of the FeSe superconductor.…”

Section: Introductionsupporting

confidence: 69%

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

2020

View full text Add to dashboard Cite

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:

show abstract

Quantum Vortex Core and Missing Pseudogap in the Multiband BCS-BEC Crossover Superconductor FeSe

Cited by 73 publications

References 22 publications

Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC crossover in a two-band Fermi gas

Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC crossover in a two-band Fermi gas

Screening of pair fluctuations in superconductors with coupled shallow and deep bands: A route to higher-temperature superconductivity

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

Contact Info

Product

Resources

About