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Strong- to weak-coupling superconductivity in high-Tc bismuthates: Revisiting the phase diagram via μSR


Shang, T; Gawryluk, D J; Naamneh, M; Salman, Z; Guguchia, Z; Medarde, M; Shi, M; Plumb, N C; Shiroka, T (2020). Strong- to weak-coupling superconductivity in high-Tc bismuthates: Revisiting the phase diagram via μSR. Physical review B, 101:014508.

Abstract

Several decades after the discovery of superconductivity in bismuthates, the strength of their electron-phonon coupling and its evolution with doping remain puzzling. To clarify these issues, polycrystalline hole-doped Ba1−xKxBiO3 (0.1≤x≤0.6) samples were systematically synthesized and their bulk and microscopic superconducting properties were investigated by means of magnetic susceptibility and muon-spin rotation and relaxation (μSR), respectively. The phase diagram of Ba1−xKxBiO3 was reliably extended up to x=0.6, which is still found to be a bulk superconductor. The lattice parameter a increases linearly with K content, implying a homogeneous chemical doping. The low-temperature superfluid density, measured via transverse-field μSR, indicates an isotropic fully gapped superconducting state with zero-temperature gaps Δ0/kBTc=2.15, 2.10, and 1.75, and magnetic penetration depths λ0=219, 184, and 279 nm for x=0.3, 0.4, and 0.6, respectively. A change in the superconducting gap, from a nearly ideal BCS value (1.76kBTc in the weak-coupling case) in the overdoped x=0.6 region, to much higher values in the optimally doped case, implies a gradual decrease in electron-phonon coupling with doping.

Abstract

Several decades after the discovery of superconductivity in bismuthates, the strength of their electron-phonon coupling and its evolution with doping remain puzzling. To clarify these issues, polycrystalline hole-doped Ba1−xKxBiO3 (0.1≤x≤0.6) samples were systematically synthesized and their bulk and microscopic superconducting properties were investigated by means of magnetic susceptibility and muon-spin rotation and relaxation (μSR), respectively. The phase diagram of Ba1−xKxBiO3 was reliably extended up to x=0.6, which is still found to be a bulk superconductor. The lattice parameter a increases linearly with K content, implying a homogeneous chemical doping. The low-temperature superfluid density, measured via transverse-field μSR, indicates an isotropic fully gapped superconducting state with zero-temperature gaps Δ0/kBTc=2.15, 2.10, and 1.75, and magnetic penetration depths λ0=219, 184, and 279 nm for x=0.3, 0.4, and 0.6, respectively. A change in the superconducting gap, from a nearly ideal BCS value (1.76kBTc in the weak-coupling case) in the overdoped x=0.6 region, to much higher values in the optimally doped case, implies a gradual decrease in electron-phonon coupling with doping.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Electronic, Optical and Magnetic Materials
Physical Sciences > Condensed Matter Physics
Language:English
Date:9 January 2020
Deposited On:12 Mar 2020 14:56
Last Modified:29 Jul 2020 14:52
Publisher:American Physical Society
ISSN:2469-9950
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1103/physrevb.101.014508

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