Korringa factor in Dirac-nodal-line systems

Abstract

The Korringa factor $K(α)$ in the nuclear magnetic resonance studies is a widely used measure of electron-correlation effects in metals and is conventionally interpreted using the non-correlated value $K(α)$ = 1. In Dirac-fermion systems, however, the non-correlated reference value depends on the electronic density of states (DOS) and differs from that of conventional metals. Here, we theoretically investigate the non-correlated Korringa factor $K^*(α)$ in a Dirac nodal-line (DNL) system with finite nodal-line dispersion using a DOS-based approach. We show that $K^*(α)$ exhibits an intrinsic temperature dependence, continuously evolving from the Dirac-fermion value of 1.71 at high temperatures to the metallic value of 1 at low temperatures. The crossover temperature is found to be proportional to the nodal-line dispersion width, identified as the characteristic energy scale governing the non-correlated Korringa factor in DNL systems. We further demonstrate that Landau quantization generates singular DOS structures that strongly enhance $K^*(α)$, producing pronounced peaks even in the absence of electron correlations. In addition, $K^*(α)$ exhibits two distinct types of magnetic oscillations arising from intra-level and inter-level contributions. The latter originates from the overlap of singular points belonging to positive and negative quantum-number Landau subbands at the Fermi level and represents a unique consequence of the finite energy dispersion of a DNL. These results provide a quantitative reference for interpreting NMR experiments in DNL materials and for identifying genuine correlation effects beyond DOS-induced contributions.