Molybdenum Carbide: A Stable Topological Semimetal with Line Nodes and Triply Degenerate Points**Supported by the National Natural Science Foundation of China under Grant Nos 11504366, and the National Basic Research Program of China under Grant Nos 2015CB921503 and 2016YFE0110000.

Abstract

We propose that the hexagonal crystal form of MoC is a stable and new type of topological semimetal. It hosts an exotic Fermi surface consisting of two concentric nodal rings in the presence of spin-orbit coupling, and possesses four pairs of triply degenerate points (TDPs) in the vicinity of the Fermi energy. The coexistence of the nodal ring Fermi surface and TDPs in MoC leads to extraordinary properties such as distinguishable drumhead surface states and manipulatable new fermions, which make MoC a fertile platform for in-depth understanding of topological phenomena and a potential candidate material for topological electronic devices.