$\beta$-CuI: a Dirac semimetal without surface Fermi arcs

TL;DR

This paper predicts that $eta$-CuI is a Dirac semimetal with closed Fermi pockets instead of Fermi arcs, due to a large cubic term and small energy difference between surface and bulk Dirac points, challenging the usual topological protection concept.

Contribution

It introduces $eta$-CuI as a novel Dirac semimetal with non-topologically protected surface states, characterized by Fermi pockets instead of Fermi arcs, driven by a significant cubic term.

Findings

$eta$-CuI exhibits closed Fermi pockets instead of Fermi arcs.

The surface states are not topologically protected due to a large cubic term.

Surface and bulk Dirac points have a small energy difference.

Abstract

Anomalous surface states with Fermi arcs are commonly considered to be a fingerprint of Dirac semimetals (DSMs). In contrast to Weyl semimetals, however, Fermi arcs of DSMs are not topologically protected. Using first-principles calculations, we predict that $\beta$-CuI is a peculiar DSM whose surface states form closed Fermi pockets instead of Fermi arcs. In such a fermiological Dirac semimetal, the deformation mechanism from Fermi arcs to Fermi pockets stems from a large cubic term preserving all crystal symmetries, and the small energy difference between the surface and bulk Dirac points. The cubic term in $\beta$-CuI, usually negligible in prototypical DSMs, becomes relevant because of the particular crystal structure. As such, we establish a concrete material example manifesting the lack of topological protection for surface Fermi arcs in DSMs