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arXiv · 1412.4667

Point-contact Andreev-reflection spectroscopy in Fe(Te,Se) films: multiband superconductivity and electron-boson coupling

D. Daghero·P. Pecchio·G. A. Ummarino·F. Nabeshima·Y. Imai·A. Maeda·I. Tsukada·S. Komiya·R. S. Gonnelli
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Abstract

We report on a study of the superconducting order parameter in Fe(Te$_{1-x}$Se$_{x}$) thin films (with different Se contents: x=0.3, 0.4, 0.5) by means of point-contact Andreev-reflection spectroscopy (PCARS). The PCARS spectra show reproducible evidence of multiple structures, namely two clear conductance maxima associated to a superconducting gap of amplitude $Δ_E \simeq 2.75 k_B T_c$ and additional shoulders at higher energy that, as we show, are the signature of the strong interaction of charge carriers with a bosonic mode whose characteristic energy coincides with the spin-resonance energy. The details of some PCARS spectra at low energy suggest the presence of a smaller and not easily discernible gap of amplitude $Δ_H \simeq 1.75 k_B T_c$. The existence of this gap and its amplitude are confirmed by PCARS measurements in Fe(Te$_{1-x}$Se$_{x}$) single crystals. The values of the two gaps $Δ_E$ and $Δ_H$, once plotted as a function of the local critical temperature $T_c^A$, turn out to be in perfect agreement with the results obtained by various experimental techniques reported in literature.

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D. Daghero, P. Pecchio, G. A. Ummarino, F. Nabeshima, Y. Imai, A. Maeda, I. Tsukada, S. Komiya, R. S. Gonnelli. 2014-12-15. Point-contact Andreev-reflection spectroscopy in Fe(Te,Se) films: multiband superconductivity and electron-boson coupling. https://doi.org/10.1088/0953-2048%2F27%2F12%2F124014.

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