Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet

TL;DR

This study reveals that in EuCd2As2, ferromagnetic order selectively enhances quasiparticle lifetimes in certain bands, driven by band splitting and multi-orbital effects, with implications for spintronic devices.

Contribution

It provides the first direct observation of band-selective quasiparticle lifetime enhancement due to ferromagnetic order in a magnetic metal.

Findings

Quasiparticle lifetime increases in specific bands in the ferromagnetic state.

The enhancement is energy and momentum dependent, linked to band splitting.

Disentangling of scattering mechanisms reveals the roles of disorder and magnons.

Abstract

Electrons navigate more easily in a background of ordered magnetic moments than around randomly oriented ones. This fundamental quantum mechanical principle is due to their Bloch wave nature and also underlies ballistic electronic motion in a perfect crystal. As a result, a paramagnetic metal that develops ferromagnetic order often experiences a sharp drop in the resistivity. Despite the universality of this phenomenon, a direct observation of the impact of ferromagnetic order on the electronic quasiparticles in a magnetic metal is still lacking. Here we demonstrate that quasiparticles experience a significant enhancement of their lifetime in the ferromagnetic state of the low-density magnetic semimetal EuCd2As2, but this occurs only in selected bands and specific energy ranges. This is a direct consequence of the magnetically induced band splitting and the multi-orbital nature of the material. Our detailed study allows to disentangle different electronic scattering mechanisms due to non-magnetic disorder and magnon exchange. Such high momentum and energy dependence quasiparticle lifetime enhancement can lead to spin selective transport and potential spintronic applications.