T. Klein

Point-contact spectroscopy of MgB2

Abstract Point-contact spectroscopy measurements on magnesium diboride reveal the existence of two superconducting energy gaps closing at the same transition temperature in line with the multi-band model of superconductivity. The sizes of the two gaps ( Δ π =2.8 meV and Δ σ =6.5–7 meV) are respectively smaller and larger than the expected weak coupling value of the one-gap superconductor. The smaller gap is rapidly filled by a small magnetic field of about 1–2 T much lower than the real upper critical field H c2 . The larger gap is closed at the anisotropic H c2 . Above the gap energies reproducible non-linearities are observed at the characteristic phonon energies of MgB 2 .