Observation of phonon structure in electron density of states of normal metal

TL;DR

This paper demonstrates that phonon structures can be observed in the electron density of states of normal metals when finite electronic bandwidth effects are considered, especially in narrow band materials like K3C60.

Contribution

It shows that finite bandwidth effects enable phonon structures to appear in the normal state EDOS, challenging the standard view that they are only visible in the superconducting state.

Findings

Finite bandwidth leads to observable phonon features in EDOS.

Photoemission spectroscopy can resolve these phonon structures in narrow band metals.

Finite band effects are significant in materials like K3C60.

Abstract

Within standard treatments of the interacting electron--phonon system the electron density of states (EDOS) shows no sign of the phonons when the system is in the normal state. On the other hand, emergence of a fine energy scale in the superconducting state makes the phonons readily observable in the EDOS and other spectroscopic quantities. Here we wish to re-examine the conditions under which phonon structure might be present in the normal state. Accounting for a finite, i.e. non-infinite, electronic bandwidth results in easily distinguishable phonon structure in the EDOS. We argue that for narrow band metals, the resolution of photoemission spectroscopy is sufficient for resolving these structures. Manifestations of finite band effects in $K_3C_{60}$ are discussed.