Observation of highly anisotropic bulk dispersion and spin-polarized topological surface states in CoTe2

TL;DR

This study identifies CoTe2 as a new type-II Dirac semimetal with highly anisotropic bulk dispersion and unique out-of-plane spin-polarized topological surface states, combining theoretical calculations and experimental spectroscopy.

Contribution

It reveals the presence of type-II Dirac fermions and novel out-of-plane spin-polarized surface states in CoTe2, expanding the understanding of topological materials.

Findings

CoTe2 hosts a pair of type-II Dirac fermions around 90 meV above the Fermi energy.

Multiple topological band inversions lead to spin-polarized surface states.

Surface states exhibit out-of-plane spin polarization, unlike typical Rashba-type states.

Abstract

We present CoTe2 as a new type-II Dirac semimetal supporting Lorentz symmetry violating Dirac fermions in the vicinity of the Fermi energy. By combining first principle ab-initio calculations with experimental angle-resolved photo-emission spectroscopy results, we show the CoTe2 hosts a pair of type-II Dirac fermions around 90 meV above the Fermi energy. In addition to the bulk Dirac fermions, we find several topological band inversions in bulk CoTe2, which gives rise to a ladder of spin-polarized surface states over a wide range of energies. In contrast to the surface states which typically display Rashba-type in-plane spin splitting, we find that CoTe2 hosts novel out-of-plane spin polarization as well. Our work establishes CoTe2 as a potential candidate for the exploration of Dirac fermiology and applications in spintronic devices, infrared plasmonics, and ultrafast optoelectronics.