Semi-Dirac Fermions in a Topological Metal

Project Summary: Semi-Dirac fermions represent a peculiar class of fermions that are massless in one
direction and massive in the perpendicular direction in two-dimensions. The unique combination of massless and massive nature endowed semi-Dirac fermions with many unusual transport/optical properties. The proximity of semi-Dirac fermions to various topological phases (e.g. a Chern insulating state) has also drawn intense theoretical efforts since their prediction 16 years ago. Yet these peculiar fermions have evaded experimental detection so far. The Basov group at Columbia University with international collaborators, and 2DCC have successfully identified the defining feature of semi-Dirac fermions – 𝐵2/3 scaling of Landau levels (B, magnetic field) – in a prototypical nodal-line metal ZrSiS. Through Landau level spectroscopy, they demonstrate this characteristic 𝐵2/3 power-law behaviors in ZrSiS subject to in-plane magnetic fields. The nodal-line structures in ZrSiS feature multiple crossing points, which they identify to host semi-Dirac fermions, corroborated with ab-initio calculations and a minimum two-band model. The experimental data together with the theoretical models establish a new platform to study the exotic phenomena of merging of Dirac points.

Publication: Yinming Shao et al., Physical Review X 14, 041057 (2024)

2DCC Role:This research resulted from a close collaboration between 2DCC and Prof. Basov’s group. The 2DCC’s ability of growing high-quality ZrSiS crystals made this impactful work possible