Orbital paramagnetism without density of states enhancement in nodal-line semimetal ZrSiS

Unconventional orbital paramagnetism without enhancement of the density of states was recently discovered in the nodal-line semimetal ZrSiS. Here, we propose a novel interband mechanism of orbital paramagnetism associated with the negative curvature of energy dispersions, which successfully explains the observed anomalous orbital paramagnetism. This negative curvature arises from energy fluctuations along the nodal line, inherent in realistic nodal-line materials. Our new mechanism indicates that such orbital paramagnetism serves as strong evidence for the existence of nodal lines not only in ZrSiS but potentially in various other nodal-line materials as well.