Abstract
Three-dimensional topological semi-metals carry quasiparticle states that mimic massless relativistic Dirac fermions, elusive particles that have never been observed in nature. As they appear in the solid body, they are not bound to the usual symmetries of space-time and thus new types of fermionic excitations that explicitly violate Lorentz-invariance have been proposed, the so-called type-II Dirac fermions. We investigate the electronic spectrum of the transition-metal dichalcogenide PtSe2 by means of quantum oscillation measurements in fields up to 65 T. The observed Fermi surfaces agree well with the expectations from band structure calculations, that recently predicted a type-II Dirac node to occur in this material. A hole- and an electron-like Fermi surface dominate the semi-metal at the Fermi level. The quasiparticle mass is significantly enhanced over the bare band mass value, likely by phonon renormalization. Our work is consistent with the existence of type-II Dirac nodes in PtSe2, yet the Dirac node is too far below the Fermi level to support free Dirac–fermion excitations.
Highlights
Band structure theory is one of the most successful concepts in condensed matter physics, classifying solids into metals and insulators
It was shown that the generalization of the Dirac equation to condensed matter systems has solutions that cannot appear in elementary particles as they are forbidden by Lorentz symmetry [7]
The electronic system of the semi-metal PtSe2 is dominated by a larger hole pocket and two small electron pockets, and our results experimentally confirm the band structure calculations of [12]
Summary
Three-dimensional topological semi-metals carry quasiparticle states that mimic massless relativistic author(s) and the title of the work, journal citation Dirac fermions, elusive particles that have never been observed in nature. As they appear in the solid and DOI. The observed Fermi surfaces agree well with the expectations from band structure calculations, that recently predicted a type-II Dirac node to occur in this material. A hole- and an electron-like Fermi surface dominate the semi-metal at the Fermi level. Our work is consistent with the existence of type-II Dirac nodes in PtSe2, yet the Dirac node is too far below the Fermi level to support free Dirac–fermion excitations
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