NMR verification of Dirac nodal lines in a single-component molecular conductor

TL;DR

This study uses NMR experiments and simulations to confirm the presence of Dirac nodal lines in a molecular conductor, revealing effects of electron correlation and Landau quantization on these exotic electronic states.

Contribution

First demonstration of NMR verification of Dirac nodal lines in a molecular material, linking experimental data with theoretical models to understand correlation effects.

Findings

NMR spectral shift and relaxation rates match DNL predictions

Suppression of Fermi velocity observed due to electron correlation

Enhanced antiferromagnetic fluctuations linked to Landau quantization

Abstract

The Dirac nodal line (DNL) is a novel form of massless Dirac fermions that reside along lines in momentum space. Here, we verify genuine DNLs in the molecular material, [Ni(dmdt)$_2$], with the combined NMR experiments and numerical simulations. The NMR spectral shift and spin-lattice relaxation rate divided by temperature, $1/T_1T$, decrease linearly and quadratically with temperature, respectively, and become constant at low temperatures, consistent with slightly dispersive DNLs with small Fermi pockets. Comparison of these results with model simulations of DNLs reveals the suppression of the Fermi velocity and the enhancement of antiferromagnetic fluctuations due to electron correlation as well as the influence of the Landau quantization. The present study offers a demonstration to identify the DNL and evaluate the correlation effect with NMR.