Peter J. Szabo

Magnetic properties and gap formation in FeSi

Abstract Magnetisation, magnetic susceptibility, resistivity, optical-reflectivity and point-contact tunnelling measurements were used to study an FeSi single crystal. Magnetisation measurements revealed a ferromagnetic contribution which is more pronounced below 100 K. Magnetic susceptibility, resistivity, far-infrared and point-contact data are consistent with the characterisation of FeSi as a narrow-gap semiconductor or Kondo insulator. Fits to our transport data suggest the formation of a gap at about Eg ≈ 650 K and a fit to our susceptibility data indicates a gap at about Eg ≈ 1200 K. The point-contact gap is filled at about 60 K. Optical spectra show a significant reduction of the low frequency reflectivity below 200 K.

From superconducting to normal density of states of Ba1−xKxBiO3 by tunneling in high magnetic fields

Abstract The tunneling effect in the superconducting Ba 1−x K x BiO 3 , where x=0.4, has been measured in a magnetic field up to 20T. In the BCS-like tunneling conductance we have observed the pair-breaking effect of the field leading to a decrease of the superconducting energy gap. In the applied magnetic field the observed phonon-like anomalies in the tunneling spectra are decreased and smeared out together with the energy-gap structure, pointing to the phonon mediated pairing mechanism for the superconductivity in the system.

Point-contact spectroscopy of YNi5

Abstract PC spectra of YNi 5 intermetallic compound homocontacts and heterocontacts with Cu have been measured in the ballistic regime. Phonon maxima at characteristic energies of 4, 8, 18 and 30 meV have been observed in the electron-phonon interaction function. The phonon parts of PC spectra of RENi 5 (RE  La, Ce, Pr, Sm, Y) compounds with isomorphous lattice structure are similar which corresponds to small differences between lattice constants of these materials.