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BCS superconductivity near the band edge: Exact results for one and several bands

D. Valentinis, D. van der Marel, C. Berthod

DOI 10.1103/PhysRevB.94.024511 · Physical Review B

T1

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Abstract

We revisit the problem of a BCS superconductor in the regime where the Fermi energy is smaller than the Debye energy. This regime is relevant for low-density superconductors such as SrTiO3 that are not in the BEC limit, as well as in the problem of “shape resonances” associated with the confinement of a three-dimensional superconductor. While the problem is not new, exact results were lacking in the low-density limit. In two dimensions, we find that the initial rise of the pairing temperature Tc at low density n is nonanalytic and faster than any power of n. In three dimensions, we also find that Tc is nonanalytic, but starts with zero slope at weak coupling and infinite slope at strong coupling. Self-consistent treatment of the chemical potential and energy dependence of the density of states are crucial ingredients to obtain these results. We also present exact results for multiband systems and confirm our analytical expressions by numerical simulations.

Source-reported materials — not catalogue approval

FormulaReported Tc (K)Pressure (GPa)Type
SrTiO3

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—Pressure not reportedunknown
LaAlO3/SrTiO3

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Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.

—Pressure not reportedunknown

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