Two regimes in the magnetic field response of superconducting MgB$_2$

TL;DR

This study uses scanning tunneling microscopy to investigate the superconducting phase diagram of MgB$_2$, revealing two distinct regimes in the magnetic field response of its $eta$-band and elucidating the interplay between intra- and inter-band effects.

Contribution

It uncovers two regimes in the magnetic field response of MgB$_2$'s $eta$-band and clarifies the roles of intrinsic superconductivity and inter-band coupling in its DOS behavior.

Findings

Rapid filling of the DOS gap up to 0.5 T

Persistence of the gap up to 2 T

Evidence of two terms in the DOS: intrinsic and inter-band coupling

Abstract

Using Scanning Tunneling Microscope at low temperature we explore the superconducting phase diagram in the $\pi$-band of the two-band superconductor MgB$_2$. In this band the peculiar shape of the local tunneling spectra and their dynamics in the magnetic field reveal the complex character of the quasiparticle density of states (DOS). The gap in the DOS is first rapidly filled with states in raising the magnetic field up to 0.5 T and then slowly approaches the normal state value : The gap is observed up to 2 T. Such a change in the DOS dynamics suggests the existence of two terms in the DOS of the $\pi$-band: a first one, reflecting an intrinsic superconductivity in the band and a second one, originating from an inter-band coupling to the $\sigma$-band. Our findings allow a deeper understanding of the unique phase diagram of MgB$_2$.