Evidence for Dirac Nodes from Quantum Oscillations in SrFe$_2$As$_2$

TL;DR

This study uses quantum oscillations in SrFe$_2$As$_2$ to identify evidence of Dirac nodes, revealing deviations from parabolic band behavior indicative of Dirac dispersion near the Fermi level.

Contribution

It provides experimental evidence for Dirac nodes in SrFe$_2$As$_2$ through detailed quantum oscillation measurements and analysis.

Findings

Observation of multiple Fermi surface pockets.

Deviation from expected mass-to-frequency ratio for one orbit.

Identification of a band with Dirac dispersion near the Fermi level.

Abstract

We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe$_2$As$_2$ as the angle between the applied magnetic field and crystalline axes is varied. Our measurements were performed on high quality single crystals in a superconducting magnet, and in pulsed magnetic fields up to 60 T, allowing us to observe orbits from several small Fermi surface pockets. We extract the cyclotron effective mass $m^{\star}$ and frequency $F$ for these orbits and track their values as the field is rotated away from the c-axis. While a constant ratio of $m^{\star}/F$ is observed for one orbit as expected for a parabolic band, a clear deviation is observed for another. We conclude that this deviation points to an orbit derived from a band with Dirac dispersion near the Fermi level.