Electron-hole tunneling revealed by quantum oscillations in the nodal-line semimetal HfSiS

TL;DR

This study reveals quantum oscillations in HfSiS indicating electron-hole tunneling, confirmed by a unique 'figure of eight' orbit, demonstrating Klein tunneling in a topological semimetal.

Contribution

First experimental observation of Klein tunneling in a nodal-line semimetal via quantum oscillations and magnetic breakdown.

Findings

Observation of 'figure of eight' oscillation confirming Klein tunneling

Cyclotron mass of combined orbit matches theoretical predictions

Oscillation intensity decreases with misaligned magnetic field

Abstract

We report a study of quantum oscillations in the high-field magneto-resistance of the nodal-line semimetal HfSiS. In the presence of a magnetic field up to 31 T parallel to the c-axis, we observe quantum oscillations originating both from orbits of individual electron and hole pockets, and from magnetic breakdown between these pockets. In particular, we find an oscillation associated with a breakdown orbit enclosing one electron and one hole pocket in the form of a `figure of eight'. This observation represents an experimental confirmation of the momentum space analog of Klein tunneling. When the c-axis and the magnetic field are misaligned with respect to one another, this oscillation rapidly decreases in intensity. Finally, we extract the cyclotron masses from the temperature dependence of the oscillations, and find that the mass of the 'figure of eight' orbit corresponds to the sum of the individual pockets, consistent with theoretical predictions for Klein tunneling in topological semimetals.