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Abstract: A series of I(V) characteristics and bias-dependent differential resistance dV/dI(V) curves of point contacts made between a single crystal of two-band superconductor MgB2 and Cu were measured in magnetic fields up to 9T. The magnetic field dependences of the excess current in the I(V) curves were obtained and analyzed using Koshelev and Golubov''s [Phys. Rev. Lett. 90, 177002 (2003)] theoretical results for the mixed state of a dirty two-band superconductor. Introducing a simple model for the excess current in the point contact in the mixed state, our data can be qualitatively described using the theoretical magnetic field dependence of the superconducting order parameter of the σ and π-bands and the averaged electronic density of states in MgB2. [Copyright &y& Elsevier]

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 λ PC 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 T c ≃8.5K reveals two different superconducting (SC) states separated by K which is close to the Néel temperature T N ≃5.3K. Below the gap Δ in HoNi2B2C exhibits a standard single-band BCS-like behavior with . Above the gap features in PC spectra are strongly suppressed pointing to a peculiar SC state between and T c, where incommensurate magnetic order develops. [Copyright &y& Elsevier]

Abstract: An overview of the recent efforts in point-contact (PC) spectroscopy of the nickel borocarbide superconductors RNi2B2C in the normal and superconducting (SC) state is given. The results of measurements of the PC electron–boson(phonon) interaction spectral function are presented. Phonon maxima and crystalline-electric-field (CEF) excitations are observed in the PC spectra of compounds with R =Dy, Ho, Er and Tm, while for R =Y a dominant phonon maximum around 12meV is characteristic. Additionally, non-phonon and non-CEF maxima are observed near 3meV in R =Ho and near 6meV in R =Dy. Directional PC study of the SC gap gives evidence for the multi-band nature of superconductivity in R =Y, Lu. At low temperature the SC gap in R =Ho exhibits a standard single-band BCS-like dependence, which vanishes above , where a specific magnetic ordering starts to play a role. For R =Tm (T c ≃10.5K) a decrease of the SC gap is observed below 5K. [Copyright &y& Elsevier]

Experimental conductance histograms for Na nanowires are analyzed in detail and compared to recent theoretical results on the stability of cylindrical and elliptical nanowires, using the free-electron model. We find a one-to-one correspondence between the peaks in the histograms and the most stable nanowire geometries, indicating that several of the commonly observed nanowires have elliptical cross sections. [Copyright &y& Elsevier]