Gap-opening transition in Dirac semimetal ZrTe$_5$

TL;DR

This study uses $^{125}$Te NMR spectroscopy to reveal a gap-opening transition and spin-polarized carrier behavior in the Dirac semimetal ZrTe$_5$, providing insights into its quantum phases and electronic structure.

Contribution

It presents the first NMR evidence of a gap-opening transition and spin polarization effects in ZrTe$_5$, advancing understanding of its quantum phenomena.

Findings

Abrupt drop in relaxation rate at 150 K indicating gap opening

Negative shift below 50 K suggesting spin-polarized Dirac level repopulation

No evidence of charge density wave in the studied regime

Abstract

We apply $^{125}$Te nuclear magnetic resonance (NMR) spectroscopy to investigate the Dirac semimetal ZrTe$_5$. With the NMR magnetic field parallel to the $b$-axis, we observe significant quantum magnetic effects. These include an abrupt drop at 150 K in spin-lattice relaxation rate. This corresponds to a gap-opening transition in the Dirac carriers, likely indicating the onset of excitonic pairing. Below 50 K, we see a more negative shift for the Te$_z$ bridging site indicating the repopulation of Dirac levels with spin polarized carriers at these temperatures. This is the previously reported 3D quantum Hall regime; however, we see no sign of a charge density wave as has been proposed.