Evidence of topological edge states in a superconducting nonsymmorphic nodal-line semimetal

TL;DR

This paper presents evidence of topological edge states in a superconducting, nonsymmorphic nodal-line semimetal CaSn, combining experimental and theoretical methods to reveal potential for exotic electronic states and topological superconductivity.

Contribution

It demonstrates the existence of topological edge states in a layered superconducting material CaSn, a nonsymmorphic nodal-line semimetal, supported by ARPES, STM/STS, and ab initio calculations.

Findings

Observation of topological edge states in CaSn

Agreement between ARPES measurements and calculations

Signatures of topological edge states at surface step edges

Abstract

Topological materials host fascinating low dimensional gapless states at the boundary. As a prominent example, helical topological edge states (TESs) of two-dimensional topological insulators (2DTIs) and their stacked three-dimensional (3D) equivalent, weak topological insulators (WTIs), have sparked research enthusiasm due to their potential application in the next generation of electronics/spintronics with low dissipation. Here, we propose layered superconducting material CaSn as a WTI with nontrivial Z2 as well as nodal line semimetal protected by crystalline non-symmorphic symmetry. Our systematic angle-resolved photoemission spectroscopy (ARPES) investigation on the electronic structure exhibits excellent agreement with the calculation. Furthermore, scanning tunnelling microscopy/spectroscopy (STM/STS) at the surface step edge shows signatures of the expected TES. These integrated evidences from ARPES, STM/STS measurement and corresponding ab initio calculation strongly support the existence of TES in the non-symmorphic nodal line semimetal CaSn, which may become a versatile material platform to realize multiple exotic electronic states as well as topological superconductivity.