Observation of Effective Pseudospin Scattering in ZrSiS

TL;DR

This study uses Fourier transform scanning tunneling spectroscopy to observe pseudospin scattering phenomena in ZrSiS, revealing pseudospin conservation near the line node and energy-dependent pseudospin flips caused by specific scatterers, advancing understanding of topological semimetals.

Contribution

First direct observation of pseudospin scattering effects in ZrSiS using FT-STS, highlighting defect-induced pseudospin flips and their implications for electronic transport.

Findings

Pseudospin conservation observed near the line node.

Certain scatterers induce energy-dependent pseudospin flips.

Fermi velocity measured as 2.65 eV·Å in the Γ-M direction.

Abstract

3D Dirac semimetals are an emerging class of materials that possess topological electronic states with a Dirac dispersion in their bulk. In nodal-line Dirac semimetals, the conductance and valence bands connect along a closed path in momentum space, leading to the prediction of pseudospin vortex rings and pseudospin skyrmions. Here, we use Fourier transform scanning tunneling spectroscopy (FT-STS) at 4.5 K to resolve quasiparticle interference (QPI) patterns at single defect centers on the surface of the line nodal semimetal zirconium silicon sulfide (ZrSiS). Our QPI measurements show pseudospin conservation at energies close to the line node. In addition, we determine the Fermi velocity to be $\hbar v_F = 2.65 \pm 0.10$ eV {\AA} in the {\Gamma}-M direction ~300 meV above the Fermi energy $E_F$, and the line node to be ~140 meV above $E_F$. More importantly, we find that certain scatterers can introduce energy-dependent non-preservation of pseudospins, giving rise to effective scattering between states with opposite valley pseudospin deep inside valence and conduction bands. Further investigations of quasiparticle interference at the atomic level will aid defect engineering at the synthesis level, needed for the development of lower-power electronics via dissipationless electronic transport in the future.