Rise and fall of shape resonances in thin films of BCS superconductors

Valentinis, Davide; Marel, D. van der; Berthod, Christophe

doi:10.1103/physrevb.94.054516

Cited by 32 publications

(55 citation statements)

References 63 publications

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“…The interaction is the same in both bands and we neglect interband coupling, for simplicity. In this model, for V independent of the density n, the critical temperature can only increase with increasing n [34,35], in contradiction with the observations [6,7]. To explain the dome, V must drop with increasing n [7].…”

Section: Two-band Model For Bulk Stocontrasting

confidence: 69%

“…1(a) into a square potential well of width L and depth U , following Ref. [26]. This leads to the formation of 2D subbands at energies that depend on L and U .…”

Section: Critical Temperature Of Sto Carriers Confined In a Squarmentioning

confidence: 99%

“…[7] on top of the continuous T c (n) curve resulting from that interpolation. The calculation takes full account of the energy-dependent density of states, including the fact that E F <hω D , and uses the self-consistent chemical potential calculated at T c [35]. With this parametrization the heavy band starts to be populated before the first maximum of the double dome, as shown by quantum oscillations [7].…”

Section: Two-band Model For Bulk Stomentioning

confidence: 99%

“…We do not expect qualitative changes in our conclusions upon going from a square to a triangular or self-consistent confinement potential. The square well, moreover, has the advantage that the pairing matrix elements are known analytically [26]. The only unknown parameter of our model is therefore U , whose order of magnitude is estimated from first-principles calculations to be a few tens of meV [43].…”

Section: Critical Temperature Of Sto Carriers Confined In a Squarmentioning

confidence: 99%

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Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

et al. 2017

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Superconductivity develops in bulk doped SrTiO 3 and at the LaAlO 3 /SrTiO 3 interface with a dome-shaped density dependence of the critical temperature T c , despite different dimensionalities and geometries. We propose that the T c dome of LaAlO 3 /SrTiO 3 is a shape resonance due to quantum confinement of superconducting bulk SrTiO 3 . We substantiate this interpretation by comparing the exact solutions of a three-dimensional and quasi-two-dimensional two-band BCS gap equation. This comparison highlights the role of heavy bands for T c in both geometries. For bulk SrTiO 3 , we extract the density dependence of the pairing interaction from the fit to experimental data. We apply quantum confinement in a square potential well of finite depth and calculate T c in the confined configuration. We compare the calculated T c to transport experiments and provide an explanation as to why the optimal T c 's are so close to each other in two-dimensional interfaces and the three-dimensional bulk material.

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Section: Two-band Model For Bulk Stocontrasting

confidence: 69%

“…1(a) into a square potential well of width L and depth U , following Ref. [26]. This leads to the formation of 2D subbands at energies that depend on L and U .…”

Section: Critical Temperature Of Sto Carriers Confined In a Squarmentioning

confidence: 99%

Section: Two-band Model For Bulk Stomentioning

confidence: 99%

Section: Critical Temperature Of Sto Carriers Confined In a Squarmentioning

confidence: 99%

See 2 more Smart Citations

Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

et al. 2017

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“…Theoretical proposals have been put forward that strong T c enhancement can be achieved close to Lifshitz transition in striped 32,33 and layered systems 34 . Superconductivity in two-band models close to a Lifshitz transition is also being studied 27,35,36 . Recent experiments on monolayer FeSe 37 do suggest enhancement of superconductivity by a Lifshitz transition.…”

Section: Introductionmentioning

confidence: 99%

s+is superconductivity with incipient bands: Doping dependence and STM signatures

et al. 2017

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Motivated by the recent observations of small Fermi energies and comparatively large superconducting gaps, present also on bands not crossing the Fermi energy (incipient bands) in iron-based superconductors, we analyze the doping evolution of superconductivity in a four-band model across the Lifshitz transition including BCS-BEC crossover effects on the shallow bands. Similar to the BCS case, we find that with hole doping the phase difference between superconducting order parameters of the hole bands change from 0 to π through an intermediate s + is state, breaking time-reversal symmetry (TRS). The transition, however, occurs in the region where electron bands are incipient and chemical potential renormalization in the superconducting state leads to a significant broadening of the s + is region. We further present the qualitative features of the s + is state that can be observed in scanning tunneling microscopy (STM) experiments, also taking incipient bands into account.

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Constraints on the total coupling strengthto bosons in the iron based superconductors

Drechsler

Johnston

Grinenko

et al. 2017

Phys. Status Solidi B

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Despite the fact that the Fe-based superconductors (FeSCs) were discovered nearly ten years ago, the community is still devoting a tremendous effort towards elucidating their relevant microscopic pairing mechanism(s) and interactions. At present, there is still no consistent interpretation of their normal state properties, where the strength of the electron-electron interaction and the role of correlation effects are under debate. Here, we examine several common materials and illustrate various problems and concepts that are generic for all FeSCs. Based on empirical observations and qualitative insight from density functional theory, we show that the superconducting and low-energy thermodynamic properties of the FeSCs can be described semi-quantitively within multiband Eliashberg theory. We account for an important high-energy mass renormalization phenomenologically, and in agreement with constraints provided by thermodynamic, optical, and angle-resolved photoemission data. When seen in this way, all FeSCs with T c < 40 K studied so far are found to belong to an intermediate coupling regime. This finding is in contrast to the strong coupling scenarios proposed in the early period of the FeSC history. We also discuss several related issues, including the role of band shifts as measured by the positions of van Hove singularities, and the nature of a recently suggested quantum critical point in the strongly hole-doped systems AFe 2 As 2 (A = K, Rb, Cs). Using high-precision full relativistic GGA-band structure calculations, we arrive at a somewhat milder mass renormalization in comparison with previous studies. From the calculated mass anisotropies of all Fermi surface sheets, only the ε-pocket near the corner of the BZ is compatible with the experimentally observed anisotropy of the upper critical field, pointing to its dominant role in the superconductivity of these three compounds.

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Rise and fall of shape resonances in thin films of BCS superconductors

Cited by 32 publications

References 63 publications

Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

s+is superconductivity with incipient bands: Doping dependence and STM signatures

Constraints on the total coupling strengthto bosons in the iron based superconductors

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