Stabilization of the vortex-liquid state by strong pairing interaction

Adachi, Kyosuke; Ikeda, Ryusuke

doi:10.1103/physrevb.99.064508

Cited by 5 publications

(3 citation statements)

References 48 publications

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“…The k F ξ value of the order of unity signifies that the pairing is BEC-like, while the value of several tens points to BCS-like pairing, thus demonstrating that pressure induces a BEC-to-BCS crossover. The field-robust vortex liquid state and fluctuations at low pressures are consistent with the short coherence length and small density of the bosonic pairs inherent in BEC-like pairing, as shown theoretically [46]. ∇ x T under a perpendicular magnetic field induces a transverse electric field E y (see the inset of Fig.…”

Section: B Upper Critical Field and Superconducting Coherence Length ...supporting

confidence: 82%

Mott-driven BEC-BCS crossover in a doped spin liquid candidate, kappa-(BEDT-TTF)4Hg2.89Br8

Suzuki,

Wakamatsu,

Ibuka

et al. 2022

Preprint

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The pairing of interacting fermions leading to superfluidity has two limiting regimes: the Bardeen-Cooper-Schrieffer (BCS) scheme for weakly interacting degenerate fermions and the Bose-Einstein condensation (BEC) of bosonic pairs of strongly interacting fermions. While the superconductivity that emerges in most metallic systems is the BCS-like electron pairing, strongly correlated electrons with poor Fermi liquidity can condense into the unconventional BEC-like pairs. Quantum spin liquids harbor extraordinary spin correlation free from order and the superconductivity that possibly emerges by carrier doping of the spin liquids is expected to have a peculiar pairing nature. The present study experimentally explores the nature of the pairing condensate in a doped spin-liquid candidate material and under varying pressure, which changes the electron-electron Coulombic interactions across the Mott critical value in the system. The transport measurements reveal that the superconductivity at low pressures is a BEC-like condensate from a non-Fermi liquid and crosses over to a BCS-like condensate from a Fermi liquid at high pressures. The Nernst-effect measurements distinctively illustrate the two regimes of the pairing in terms of its robustness to the magnetic field. The present Mott tuning of the BEC-BCS crossover can be compared to the Feshbach tuning of the BEC-BCS crossover of fermionic cold atoms. I. INTRODUCTIONStrong interactions between itinerant electrons in solids cause peculiar correlations or organizations among the electrons beyond the Fermi-liquid framework [1]. Superconductivity emerging in these circumstances can be outside the celebrated Bardeen-Cooper-Schrieffer (BCS) framework, which assumes an instability of Fermi surfaces formed by degenerate fermions with well-defined momenta [2], in that the strong correlation of electrons makes their momenta ill-defined and the electron pairing in momentum space, the central idea of BCS theory, is less pertinent. In this case, superconductivity is of the Bose-Einstein condensation (BEC) type, as the size of Cooper pairs is as small as their mean distance, or equivalently, the interaction energy is comparable to the Fermi energy. Several unconventional superconductors have been discussed in the framework of a BEC scenario [3][4][5][6][7]. More broadly, the superfluidity of cold fermionic atoms is known to be controllable between the BEC and BCS regimes by the magnetic-field tuning of the interatomic interaction through

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Section: B Upper Critical Field and Superconducting Coherence Length ...supporting

confidence: 82%

Mott-driven BEC-BCS crossover in a doped spin liquid candidate, kappa-(BEDT-TTF)4Hg2.89Br8

Suzuki,

Wakamatsu,

Ibuka

et al. 2022

Preprint

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show abstract

“…Clearly, the deviation from the concave melting curve suggesting the n = 0 LL scaling [14,18] is due to moderately strong PPB, and the region in which the n = 0 LL scaling is visible is limited to the low field range close to T c0 . It has been argued elsewhere [25] that the low field behavior of the melting line is also affected by the strong-coupling effect due to the SC fluctuation itself in a system close to the so-called BCS-BEC crossover regime.…”

Section: Summary and Discussionmentioning

confidence: 97%

Vortex Lattice Melting Line in Superconductors with Paramagnetic Pair-Breaking

Nakashima,

Ikeda

2022

Preprint

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Recent experiments on the Iron-based superconductor FeSe in a high magnetic field have suggested the presence of both the fluctuation-induced vortex liquid regime and a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex lattice. To get a general picture on the magnetic phase diagram in type II superconductors with strong superconducting (SC) fluctuation and strong paramagnetic pair-breaking (PPB) such as FeSe, the vortex lattice melting curve Hm(T ) is theoretically investigated in the situations where a FFLO state is expected to occur. In general, PPB tends to narrow the vortex liquid regime intervening between Hc2(T ) and Hm(T ). In particular, the vortex liquid regime is found to rapidly shrink upon entering, by cooling, the temperature range in which the FFLO state with a periodic modulation parallel to the magnetic field is stable in the mean field theory. Based on the present results, the high field SC phase diagrams of FeSe in the parallel and perpendicular field configurations are discussed.

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“…Clearly, the deviation from the concave melting curve 024508-6 suggesting the n = 0 LL scaling [14] is due to moderately strong PPB, and the region in which the n = 0 LL scaling is correctly seen is limited to the low-field range close to T c0 . It has been argued elsewhere [25] that the low-field behavior of the melting line is also affected by the strong-coupling effect due to the SC fluctuation itself in a system close to the so-called BCS-BEC crossover regime.…”

Section: Summary and Discussionmentioning

confidence: 98%

Vortex lattice melting line in superconductors with paramagnetic pair breaking

Nakashima

Ikeda

2022

Phys. Rev. B

Self Cite

View full text Add to dashboard Cite

Recent experiments on the iron-based superconductor FeSe in a high magnetic field have suggested the presence of both the fluctuation-induced vortex liquid regime and a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex lattice. To get a general picture of the magnetic phase diagram in type II superconductors with strong superconducting (SC) fluctuation and strong paramagnetic pair breaking (PPB) such as FeSe, the vortex lattice melting curve H m (T ) is theoretically investigated in situations where a FFLO state is expected to occur. In general, PPB tends to narrow the vortex liquid regime intervening between H c2 (T ) and H m (T ). In particular, the vortex liquid regime is found to rapidly shrink upon entering; by cooling, the temperature range in which the FFLO state with a periodic modulation parallel to the magnetic field is stable in mean-field theory. Based on the present results, the high-field SC phase diagrams of FeSe in the parallel and perpendicular field configurations are discussed.

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Stabilization of the vortex-liquid state by strong pairing interaction

Cited by 5 publications

References 48 publications

Mott-driven BEC-BCS crossover in a doped spin liquid candidate, kappa-(BEDT-TTF)4Hg2.89Br8

Mott-driven BEC-BCS crossover in a doped spin liquid candidate, kappa-(BEDT-TTF)4Hg2.89Br8

Vortex Lattice Melting Line in Superconductors with Paramagnetic Pair-Breaking

Vortex lattice melting line in superconductors with paramagnetic pair breaking

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