Peculiarities of the superconducting gaps and the electron-boson interaction in TmNi2B2C as seen by point-contact spectroscopy

Abstract

Point-contact (PC) investigations on the title compound in the normal and superconducting (SC) state (Tc=10,6 K) are presented. The temperature dependence of the SC gap of TmNi2B2C determined from Andreev-reflection (AR) spectra using the standard single-gap approximation (SGA) deviates from the BCS behavior in displaying a maximum at about Tc/2. A refined analysis within the two-gap approximation provides evidence for the presence of a second gap twice as large as the main gap (the first one), while the latter is close to that within the SGA. This way, TmNi2B2C expands the number of nickel borocarbide superconductors which exhibit a clear multiband character. Additionally, for the first time "reentrant" features were found in the AR spectra for some PCs measured in a magnetic field. The PC spectroscopy of the electron-boson interaction in TmNi2B2C in the normal state reveals a pronounced phonon maximum at 9.5meV and a more smeared one around 15 meV, while at higher energies the PC spectra are almost featureless. Additionally, the most intense peak slightly above 3meV observed in the PC spectra of TmNi2B2C is presumably caused by crystalline-electric-field (CEF) excitations. The peak near 1meV detected for some PC spectra is connected with a modification of the CEF probably due to boron or carbon vacancies, allowing to probe the local stoichiometry by PC spectroscopy.

10 two-column pages, 9 figs, to be published in PRB

References in corpus (10)

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• Point-contact study of the LuNi2B2C borocarbide superconducting film
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• Anatomy of point-contact Andreev reflection spectroscopy from the experimental point of view (review)
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• The superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy
• Non-collinear order and gapless superconductivity in s-wave magnetic superconductors
• Josephson effect and Andreev reflection in Ba(1-x)NaxFe2As2 (x=0.25 and 0.35) point contacts
• Pauli limited d-wave superconductors: Quantum breached pair phase and thermal transitions
• Sub-kelvin Andreev reflection spectroscopy of superconducting gaps in FeSe
• Superconductivity in hole-doped germanium point contacts