Ultrafast Carrier Relaxation Dynamics in a Nodal-Line Semimetal PtSn$_4$

TL;DR

This study uncovers the ultrafast relaxation of photoexcited carriers in the topological nodal-line semimetal PtSn$_4$, revealing complex scattering mechanisms and the influence of its unique electronic structure.

Contribution

It provides the first direct observation of linear bulk dispersions and ultrafast carrier dynamics in PtSn$_4$, combining experimental spectroscopy with theoretical analysis.

Findings

Ultrafast carrier relaxation occurs within a few hundred femtoseconds.

Complex multichannel electron-phonon scattering mechanisms are identified.

Unique anisotropic relaxation dynamics are linked to the nodal-line electronic structure.

Abstract

Topological Dirac nodal-line semimetals host topologically nontrivial electronic structure with nodal-line crossings around the Fermi level, which could affect the photocarrier dynamics and lead to novel relaxation mechanisms. Herein, by using time- and angle-resolved photoemission spectroscopy, we reveal the previously-inaccessible linear dispersions of the bulk conduction bands above the Fermi level in a Dirac nodal-line semimetal PtSn$_4$, as well as the momentum and temporal evolution of the gapless nodal lines. A surprisingly ultrafast relaxation dynamics within a few hundred femtoseconds is revealed for photoexcited carriers in the nodal line. Theoretical calculations suggest that such ultrafast carrier relaxation is attributed to the multichannel scatterings among the complex metallic bands of PtSn$_4$ via electron-phonon coupling. In addition, a unique dynamic relaxation mechanism contributed by the highly anisotropic Dirac nodal-line electronic structure is also identified. Our work provides a comprehensive understanding of the ultrafast carrier dynamics in a Dirac nodal-line semimetal.