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Superconductivity on the Verge of a Pressure-Induced Lifshitz Transition in CaFe2As2: an Interpretation Within the Eliashberg Theory

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Abstract

In a recent paper, we presented the first directional point-contact Andreev reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure and discussed the pressure dependence of the gaps and the critical temperature. While T c exhibits a well-known smooth dependence and a broad maximum at about 0.6 GPa, both gaps increase very sharply in a small pressure range between 0.5 and 0.6 GPa, leading to a doubling of the ratio 2Δ2/k B T c and a quadruplication of the ratio 2Δ1/k B T c , Δ1 and Δ2 being the small and large gap, respectively. This peculiar behavior is likely to be related to a sharp change in the lattice structure that, in turn, produces a 2D-3D topological transition in the hole-like Fermi surface sheet. In this work, we show that, within an effective three-band Eliashberg theory for the electron-spin fluctuation coupling (s± symmetry), these results can be rationalized as being due to a large increase of the electron-boson coupling, which mimics the effects of a boost mechanism for the coupling related to the underlying Lifshitz transition.

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Funding

G.A.U. acknowledges support from the MEPhI Academic Excellence Project (Contract No. 02.a03.21.0005).

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Authors and Affiliations

  1. Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy

    G. A. Ummarino, D. Daghero, M. Tortello & R. S. Gonnelli

  2. National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moskva, 115409, Russia

    G. A. Ummarino & D. Daghero

Authors
  1. G. A. Ummarino
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  2. D. Daghero
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  3. M. Tortello
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  4. R. S. Gonnelli
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Correspondence to G. A. Ummarino.

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Ummarino, G.A., Daghero, D., Tortello, M. et al. Superconductivity on the Verge of a Pressure-Induced Lifshitz Transition in CaFe2As2: an Interpretation Within the Eliashberg Theory. J Supercond Nov Magn 31, 771–776 (2018). https://doi.org/10.1007/s10948-017-4319-7

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  • DOI: https://doi.org/10.1007/s10948-017-4319-7

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