Point-contact spectroscopy of MgB2

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 (<f>Δπ=2.8</f> meV and <f>Δσ=6.5–7</f> 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 <f>Hc2</f>. The larger gap is closed at the anisotropic <f>Hc2</f>. Above the gap energies reproducible non-linearities are observed at the characteristic phonon energies of MgB2. [Copyright &y& Elsevier]