Distinct multiple fermionic states in a single topological metal

TL;DR

This study uncovers multiple coexisting fermionic states, including weak and strong topological surface states and a novel Dirac-node arc, in the topological metal Hf2Te2P through ARPES and first-principles calculations.

Contribution

It demonstrates the coexistence of different topological fermionic states within a single material, revealing new quantum phenomena in Hf2Te2P.

Findings

Coexistence of weak and strong topological surface states in Hf2Te2P

Discovery of a Dirac-node arc along a high-symmetry direction

Confirmation of surface bands protected by in-plane time-reversal invariance

Abstract

Among the quantum materials that gained interest recently are the topological Dirac/Weyl semimetals, where conduction and valence bands touch at points in reciprocal (k)-space, and the Dirac nodal-line semimetals, where these bands touch along a line or a loop in k-space. However, the coexistence of multiple fermion phases in one and the same material has not been verified yet. Using angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations, we systematically study the metallic topological quantum material, Hf2Te2P. Our investigations discover various properties that are rare and never observed in a single Dirac material. We observe the coexistence of both weak and strong topological surface states in the same material and interestingly, at the same momentum position. An one-dimensional Dirac crossing{the Dirac-node arc-along a high-symmetry direction is revealed by our first-principles calculations and confirmed by our ARPES measurements. This novel state is associated with the surface bands of a weak topological insulator protected by in-plane time-reversal invariance. Ternary compound Hf2Te2P thus emerges as an intriguing platform to study the coexistence and competition of multi-fermionic states in one material.