Ultrafast relaxation of acoustic and optical phonons in a topological nodal-line semimetal ZrSiS

TL;DR

This study uses time-resolved photoemission spectroscopy to investigate ultrafast phonon relaxation in ZrSiS, revealing distinct decay mechanisms for bulk and surface states and highlighting the role of phonon cooling in conduction.

Contribution

It provides the first detailed analysis of transient relaxation dynamics in ZrSiS, showing how optical and acoustic phonons relax differently in bulk and surface states.

Findings

Linear decay processes for phonons observed

Acoustic cooling suppressed at high temperatures

Different relaxation mechanisms for bulk and surface states

Abstract

Despite being the most studied nodal line semimetal, a clear understanding of the transient state relaxation dynamics and the underlying mechanism in ZrSiS is lacking. Using time and angle resolved photoemission spectroscopy, we study the ultrafast relaxation dynamics in ZrSiS and reveal a unique relaxation in the bulk nodal-line state which is well captured by a simple model based on optical and acoustic phonon cooling. We find linear decay processes for both optical and acoustic phonon relaxations with acoustic cooling suppressed at high temperatures. Our results reveal different decay mechanisms for the bulk and surface states and pave a way to understand the mechanism of conduction in this material.