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 22 meV and 34 meV. For the first time the pronounced high energy maxima at about 50 meV and 100 meV were resolved. Additionally, an admixture of a crystalline-electric-field (CEF) excitation with a maximum near 10 meV and a ‘magnetic’ peak near 3 meV 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 100 meV amounts about 10% for each maxima. PC Andreev reflection measurements below the critical temperature Tc ≃ 8.5 K reveals two different superconducting (SC) states separated by T c ∗ ≃ 5.6 K which is close to the Neel temperature TN ≃ 5.3 K. Below T c ∗ the gap Δ in HoNi2B2C exhibits a standard single-band BCS-like behavior with 2 Δ / k B T c ∗ ≃ 3.9 . Above T c ∗ the gap features in PC spectra are strongly suppressed pointing to a peculiar SC state between T c ∗ and Tc, where incommensurate magnetic order develops.