Distinct multiple fermionic states in a single topological metal

M Mofazzel Hosen,Klauss Dimitri,Fangcheng Chou,Madhab Neupane,Peter M Oppeneer,Christopher Sims,Ashis K Nandy,Dariusz Kaczorowski,Alex Aperis,Raman Sankar,Gyanendra Dhakal,Pablo Maldonado,Tomasz Durakiewicz,Firoza Kabir

doi:10.1038/s41467-018-05233-1

Abstract

Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetry-protected surface states cross in reciprocal space, and the Dirac nodal-line semimetals, where bulk bands touch along a line in k-space. However, the existence of multiple fermion phases in a single material has not been verified yet. Using angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations, we systematically study the metallic material Hf2Te2P and discover properties, which are unique in a single topological quantum material. We experimentally observe weak topological insulator surface states and our calculations suggest additional strong topological insulator surface states. Our first-principles calculations reveal a one-dimensional Dirac crossing—the surface Dirac-node arc—along a high-symmetry direction which is confirmed by our ARPES measurements. This novel state originates from the surface bands of a weak topological insulator and is therefore distinct from the well-known Fermi arcs in semimetals.

Highlights

Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetry-protected surface states cross in reciprocal space, and the Dirac nodal-line semimetals, where bulk bands touch along a line in k-space
The materials of the 221 family are of particular interest due to their tetradymitetype layered crystal structure, mostly found in typical 3D topological insulators (TIs) as e.g., Bi2Te3, Bi2Se3, and Sb2Te35,31,34–36, having a threefold rotation symmetry about the z-axis
The Dirac-node arc along Γ–M that originates from the topological bulk band set (A, B) is protected by the in-plane time-reversal symmetry (TRS) —a 2D analog of the conventional TRS33

Summary

Introduction

Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetry-protected surface states cross in reciprocal space, and the Dirac nodal-line semimetals, where bulk bands touch along a line in k-space. Our first-principles calculations reveal a one-dimensional Dirac crossing—the surface Dirac-node arc—along a high-symmetry direction which is confirmed by our ARPES measurements This novel state originates from the surface bands of a weak topological insulator and is distinct from the well-known Fermi arcs in semimetals. In contrast to the Dirac-node arc of unambiguous origin observed in topological line-node semimetals[32], our DFT study reveals that here it is a signature of weak topological Z2 invariants and protected by in-plane time-reversal invariance[33] This material could be the first system to realize the coexistence of both weak and strong Z2 invariants due to the presence of multiple bulk topological bands

Methods

Results

Conclusion