Advances in point-contact spectroscopy: two-band superconductor MgB2 (A review)

TL;DR

This review discusses how point-contact spectroscopy reveals the distinct behaviors of the two electronic bands in MgB2, a high-temperature superconductor, highlighting their anisotropy, electron-phonon interactions, and the correlation with superconducting gaps.

Contribution

It provides a comprehensive analysis of PCS data on MgB2, elucidating the properties of its two electronic bands and their role in high-Tc superconductivity, including comparisons with other diborides.

Findings

Distinct behaviors of $\sigma$ and $\pi$ bands in MgB2 revealed by PCS

Correlation between superconducting gap and boron vibration mode

Comparison of PCS data with nonsuperconducting diborides

Abstract

Analysis of the point-contact spectroscopy (PCS) data on the new dramatic high-T$_c$ superconductor MgB$_2$ reveals quite different behavior of two disconnected $\sigma$ and $\pi$ electronic bands, deriving from their anisotropy, different dimensionality, and electron-phonon interaction. PCS allows direct registration of both the superconducting gaps and electron-phonon-interaction spectral function of the two-dimensional $\sigma$ and three-dimensional $\pi$ band, establishing correlation between the gap value and intensity of the high-T$_c$ driving force -- the $E_{2g}$ boron vibration mode. PCS data on some nonsuperconducting transition-metal diborides are surveyed for comparison.