Semi-Dirac Fermions in a Topological Metal

Abstract

Topological semimetals with massless Dirac and Weyl fermions represent the forefront of quantum materials research. In two dimensions (2D), a peculiar class of fermions that are massless in one direction and massive in the perpendicular direction was predicted sixteen years ago. These highly exotic quasiparticles - the semi-Dirac fermions - ignited intense theoretical and experimental interest but remain undetected. Using magneto-optical spectroscopy, we demonstrate the defining feature of semi-Dirac fermions - $B^{2/3}$ scaling of Landau levels - in a prototypical nodal-line metal ZrSiS. In topological metals, including ZrSiS, nodal-lines extend the band degeneracies from isolated points to lines, loops or even chains in the momentum space. With $\text{ab initio}$ calculations and theoretical modeling, we pinpoint the observed semi-Dirac spectrum to the crossing points of nodal-lines in ZrSiS. Crossing nodal-lines exhibit a continuum absorption spectrum but with singularities that scale as $B^{2/3}$ at the crossing. Our work sheds light on the hidden quasiparticles emerging from the intricate topology of crossing nodal-lines and highlights the potential to explore quantum geometry with linear optical responses.

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Cited by in corpus (10)

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• Crossover in Electronic Specific Heat near Narrow-Sense Type-III Dirac Cones
• Tunable plasmon modes and topological transitions in single- and bilayer semi-Dirac materials
• Unveiling three types of fermions in a nodal ring topological semimetal through magneto-optical transitions
• Fermions in $(1+2)$-dimensions modified by nonminimal coupling and its applications to condensed matter physics
• Photonic spin Hall effect dependent on Landau level transitions in monolayer WTe2
• Semi-Dirac spin liquids and frustrated quantum magnetism on the trellis lattice
• Probing imbalanced Weyl nodes in two-dimensional anisotropic Weyl semimetal via optical conductivity
• Interacting type-II semi-Dirac quasiparticles