Nodal-line semimetal HMTSF-TCNQ: Anomalous orbital diamagnetism and charge density wave

This study investigates the electronic states and physical quantities of an organic charge-transfer complex HMTSF-TCNQ, which undergoes a charge-density-wave (CDW) phase transition at temperature $T_c\simeq 30$ K. A first-principles calculation is utilized to determine that normal state topological semimetal with open nodal lines. Besed on calculation, we develop tight-binding model investigate in detail. Below $T_c$, CDW examined scheme using mean-field approximation. It shown lines are deformed into closed ones, their shapes sensitive order parameter. Using this model, theoretically evaluate dependencies two quantities: spin-lattice relaxation time $T_1$ orbital magnetic susceptibility. In particular, anomalous plateau obtained low temperatures diamagnetism. We presume originates owing conflict between interband diamagnetism, impurity scattering, line deformation. also conduct experiment magnetism, results excellent quantitative agreement theory.