Optical absorption in two-dimensional materials with tilted Dirac cones

Abstract

The interband optical absorption of linearly polarised light by two-dimensional (2D) semimetals hosting tilted and anisotropic Dirac cones in the bandstructure is analysed theoretically. Super-critically tilted (type-II) Dirac cones are characterised by an absorption that is highly dependent on the incident photon polarisation and frequency, and is tunable by changing the Fermi level with a back-gate voltage. Type-II Dirac cones exhibit open Fermi surfaces and large regions of the Brillouin zone where the valence and conduction bands sit either above or below the Fermi level. As a consequence, unlike their sub-critically tilted (type-I) counterparts, type-II Dirac cones have many states that are Pauli blocked even when the Fermi level is tuned to the level crossing point. We analyse the interplay of the tilt parameter with the Fermi velocity anisotropy, demonstrating that the optical response of a Dirac cone cannot be described by its tilt alone. As a special case of our general theory we discuss the proposed 2D type-I semimetal 8-$Pmmn$ Borophene. Guided by our in-depth analytics we develop an optical recipe to fully characterise the tilt and Fermi velocity anisotropy of any 2D tilted Dirac cone solely from its absorption spectrum. We expect our work to encourage Dirac cone engineering as a major route to create gate-tunable thin-film polarisers.

arXiv comment12 pages, 5 figures, several references added

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Cited by in corpus (12)

• Signatures of Lifshitz transition in the optical conductivity of two-dimensional tilted Dirac materials
• Photonic Topological Transitions and Epsilon-Near-Zero Surface Plasmons in Type-II Dirac Semimetal NiTe${}_2$
• Highly anisotropic optical conductivities in two-dimensional tilted semi-Dirac bands
• Optical valley separation in two-dimensional semimetals with tilted Dirac cones
• Effects of spatial dimensionality and band tilting on the longitudinal optical conductivities in Dirac bands
• Thermal difference reflectivity of tilted 2D Dirac materials
• Optical conductivity of tilted higher pseudospin Dirac-Weyl cones
• Engineering the electronic, magnetic, and optical properties of GaP monolayer by substitutional doping: a first-principles study
• Tilted Dirac Cones in Two-Dimensional Materials: Impact on Electron Transmission and Pseudospin Dynamics
• Tilted Dirac superconductor at quantum criticality: Restoration of Lorentz symmetry
• Yukawa-Lorentz Symmetry of Tilted Non-Hermitian Dirac Semimetals at Quantum Criticality
• Designer gapped and tilted Dirac cones in lateral graphene superlattices