Abstract
We report the observation of strong electron-phonon coupling in intergranular linked BiIn superconductors over an infinite range mediated by low-lying phonons. An enhanced superconducting transition temperature was observed from the magnetization, revealing a main diamagnetic Meissner state below TC(0) = 5.86(1) K and a critical field HC(0) = 1355(15) Oe with an In2Bi phase of the composite sample. The electron-phonon coupling to low lying phonons is found to be the leading mechanism for observed strong-coupling superconductivity in the BiIn system. Our findings suggest that In2Bi is in the strong-coupling region with TC(0) = 5.62(1) K, λep = 1.45, ωln = 45.92 K and α = 2.23. The estimated upper critical field can be well-described by a power law with α value higher than 2, consistent with the strong electron-phonon coupling.
Highlights
A number of electron-phonon coupled bi- and tri-metallic superconductors with enhanced superconducting transition have been discovered, renewing interest in conventional phonon-mediated superconductivity[1,2,3,4]
The maximum strong-coupling superconducting strength, α = 2.231(9), phonon energy, ωln = 45.9 K, electron-phonon coupling constant, λep = 1.453, and critical field, HC(0) = 1909(3) Oe has been estimated from pure In2Bi (y = 0.5) samples using Allen and Dynes’ formulation
The room temperature SR-X-ray diffraction (XRD) refinement carried out by using weighted analysis and superconducting measurement reveals the formation of both pure α-In (y = 0.01), In2Bi (y = 0.5) and composite α-In + In2Bi (y = 0.1–0.4), In2Bi + In5Bi3 + InBi (y = 0.6–0.7) samples, respectively
Summary
A number of electron-phonon coupled bi- and tri-metallic superconductors with enhanced superconducting transition have been discovered, renewing interest in conventional phonon-mediated superconductivity[1,2,3,4]. We consider the BiIn bimetallic system, in which Bi is a semimetal and In is a weak-coupled superconductor with transition temperature TC(0) = 3.4 K (at ambient atmosphere). When annealed together they form In2Bi, In5Bi3 and InBi bimetallic compounds and a solid solution, α-In5. A microscopic examination of polished InBi samples revealed a heterogeneous mixture of crystal grains, except for pure crystalline phases indicating granular superconductivity. In such a system, the Josephson tunneling between superconducting grains establishes inter-granular links and results in macroscopic superconductivity[7].
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