Real-space visualization of quasiparticle dephasing near the Planckian limit in the Dirac line node material ZrSiS

TL;DR

This study uses spectroscopic imaging STM to visualize quasiparticle dephasing in ZrSiS, revealing that electron-electron interactions near the Dirac line node reach the Planckian limit, indicating strong electronic correlations.

Contribution

First direct measurement of quasiparticle phase coherence length and lifetime in a Dirac line node material using spatially resolved STM imaging.

Findings

Quasiparticle lifetime below -40 meV is very short, near the Planckian limit.

Quasiparticle interference patterns decay spatially, allowing extraction of phase coherence length.

Results support the presence of strong electronic correlations near the Dirac line node.

Abstract

Dirac line node (DLN) materials are topological semimetals wherein a set of symmetry protected crossing points forms a one-dimensional (1D) line in reciprocal space. Not only are the linearly dispersing bands expected to give rise to exceptional electronic properties, but the weak screening of the Coulomb interaction near the line node may enhance electronic correlations, produce new many-body ground states, or influence the quasiparticle lifetime. We investigate the quasiparticle dynamics in the DLN material ZrSiS via spectroscopic imaging scanning tunneling microscopy (SI-STM). By studying the spatial decay of quasiparticle interference patterns (QPI) from point scatterers, we were able to directly and selectively extract the phase coherence length $l_{\textrm{QPI}}$ and lifetime $\tau_{\textrm{QPI}}$ for the bulk DLN excitations, which are dominated by inelastic electron-electron scattering. We find that the experimental $\tau_{\textrm{QPI}}(E)$ values below $-$40 meV are very short, likely due to the stronger Coulomb interactions, and lie at the Planckian limit $\hbar/|E|$. Our results corroborate a growing body of experimental reports demonstrating unusual electronic correlation effects near a DLN.