Optical valley separation in two-dimensional semimetals with tilted Dirac cones

TL;DR

This paper demonstrates that two-dimensional tilted Dirac semimetals can spatially separate carriers of different valleys under illumination, enabling optovalleytronic applications across a wide frequency range with tunable control.

Contribution

It introduces the concept of optical valley separation in tilted Dirac semimetals with preserved symmetries, expanding valleytronics to gapless systems like borophene.

Findings

Valley separation occurs at low photon frequencies including infrared and terahertz.

Full gate tunability of valley separation via Pauli blocking.

Experimental demonstration in borophene at room temperature.

Abstract

Two-dimensional semimetals with tilted Dirac cones in the electronic band structure are shown to exhibit spatial separation of carriers belonging to different valleys under illumination. In stark contrast to gapped Dirac materials this optovalleytronic phenomenon occurs in systems with intact inversion and time-reversal symmetry that host massless Dirac cones in the band structure, thereby retaining the exceptional graphene-like transport properties. As a result we demonstrate that optical valley separation is possible at arbitrarily low photon frequencies including the deep infrared and terahertz regimes with full gate tunability via Pauli blocking. As a specific example of our theory, we demonstrate tunable valley separation in the proposed two-dimensional tilted Dirac cone semimetal 8-$Pmmn$ borophene for incident infrared photons at room temperature.