Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C
Abstract
The point-contact (PC) spectroscopy study of the electron-phonon(boson) interaction (EP(B)I) spectral function in HoNi2B2C reveals phonon maxima at 16 and 22meV and 34meV. For the first time the pronounced high energy maxima at about 50meV and 100meV were resolved. Additionally, an admixture of a crystalline-electric-field (CEF) excitation with a maximum near 10meV and a `magnetic` peak near 3meV are observed. The contribution of the CEF peak in EP(B)I constant λPC is evaluated as 20-30%, while contribution of the high frequency modes at 50 and 100meV amounts about 10% for each maxima. PC Andreev reflection measurements below the critical temperature Tc=8.5K reveals two different superconducting (SC) states separated by Tc*=5.6K which is close to the Neel temperature TN=5.3K. Below Tc* the gap in HoNi2B2C exhibits a standard single-band BCS-like behavior with 2/kTc*=3.9. Above Tc* the gap features in PC spectra are strongly suppressed pointing to a peculiar SC state between Tc* and Tc, where incommensurate magnetic order develops.
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