# Role of Velocity Field and Principal Axis of Tilted Dirac Cones in Effective Hamlitonan of Non-Coplanar Nodal Loop

## TL;DR

This paper improves the effective Hamiltonian model for tilted Dirac cones on a non-coplanar nodal loop in a molecular conductor, capturing velocity variations and small energy dispersions, and analyzes related physical properties.

## Contribution

It introduces an enhanced method to accurately reproduce Dirac cone behaviors along the entire nodal loop, including velocity variations and energy dispersion.

## Key findings

- Small energy dispersion (~6 meV) among Dirac points.
- Velocity variation along the nodal line using principal axes.
- Calculated density of states and magnetic susceptibility near the chemical potential.

## Abstract

Nodal line in single-component molecular conductor [Pd(dddt)_2] has been examined to understand the tilted Dirac cone on the non-coplanar loop. In the previous work [J. Phys. Soc. Jpn. 87, 113701 (2018)], the velocity of the cone was calculated at respective Dirac points on the nodal loop based on our first-principles band structure calculations, which was a new method to derive an effective Hamiltonian with a 2 x 2 matrix. However, the Dirac cones on the nodal line are fully reproduced only at symmetric points. In the present paper, we show that our improved method well reproduces reasonable behaviors of all the Dirac cones and a very small energy dispersion of 6~meV among the Dirac points. The variation of velocities along the nodal line are shown by using principal axes of the gap function between the conduction and valence bands. Further, the density of states close to the chemical potential and orbital magnetic susceptibility are calculated using such an effective Hamiltonian.