Strong interaction between electrons and collective excitations in multiband superconductor MgB2

TL;DR

This study uses laser ARPES to reveal strong electron coupling to phonons and a potential Leggett mode in MgB2, a multiband superconductor, highlighting interactions that may influence its superconducting properties.

Contribution

It provides direct experimental evidence of electron interactions with phonons and a Leggett mode in MgB2, a multiband superconductor, using tunable laser ARPES.

Findings

Observation of a 65 meV kink due to E2g phonon coupling

Detection of a 10 meV collective mode vanishing above Tc

Strong electron-collective mode interactions in MgB2

Abstract

We use a tunable laser ARPES to study the electronic properties of the prototypical multiband BCS superconductor MgB2. Our data reveal a strong renormalization of the dispersion (kink) at ~65 meV, which is caused by coupling of electrons to the E2g phonon mode. In contrast to cuprates, the 65 meV kink in MgB2 does not change significantly across Tc. More interestingly, we observe strong coupling to a second, lower energy collective mode at binding energy of 10 meV. This excitation vanishes above Tc and is likely a signature of the elusive Leggett mode.