Symmetry dictated grain boundary state in a two-dimensional topological insulator

Abstract

Structural imperfections such as grain boundaries (GBs) and dislocations are ubiquitous in solids and have been of central importance in understanding nature of polycrystals. In addition to their classical roles, advent of topological insulators (TIs) offers a chance to realize distinct topological states bound to them. Although dislocation inside three-dimensional TIs is one of the prime candidates to look for, its direct detection and characterization are challenging. Instead, in two-dimensional (2D) TIs, their creations and measurements are easier and, moreover, topological states at the GBs or dislocations intimately connect to their lattice symmetry. However, such roles of crystalline symmetries of GBs in 2D TIs have not been clearly measured yet. Here, we present the first direct evidence of a symmetry enforced Dirac type metallic state along a GB in 1T'-MoTe${}_2$, a prototypical 2D TI. Using scanning tunneling microscope, we show a metallic state along a grain boundary with non-symmorphic lattice symmetry and its absence along the other boundary with symmorphic one. Our large scale atomistic simulations demonstrate hourglass like nodal-line semimetallic in-gap states for the former while the gap-opening for the latter, explaining our observation very well. The protected metallic state tightly linked to its crystal symmetry demonstrated here can be used to create stable metallic nanowire inside an insulator.

References in corpus (17)

• Quantum Spin Hall Effect in Graphene
• Quantum Spin Hall Effect and Topological Phase Transition in HgTe Quantum Wells
• Quantum Spin Hall Insulator State in HgTe Quantum Wells
• Linear-scaling ab-initio calculations for large and complex systems
• Realization of Quantum Spin Hall State in Monolayer 1T'-WTe2
• Dirac Semimetals in Two Dimensions
• Helical Metal Inside a Topological Band Insulator
• Hourglass Fermions
• One-dimensional Topological Edge States of Bismuth Bilayers
• Observation of Landau levels of Dirac fermions in graphite
• Observation of topological states residing at step edges of WTe2
• Imaging Quantum Spin Hall Edges in Monolayer WTe2
• Direct Visualization of 2D Topological Insulator in Single-layer 1T'-WTe2
• Universal probes of two-dimensional topological insulators: Dislocation and pi-flux
• Interplay between electronic topology and crystal symmetry: Dislocation-line modes in topological band-insulators
• Origins of the structural phase transitions in MoTe${}_2$ and WTe${}_2$
• Resolving the Topological Classification of Bismuth with Topological Defects

Cited by in corpus (10)

• Magnetic Ordering, Anomalous Lifshitz Transition and Topological Grain Boundaries in Two-Dimensional Biphenylene Network
• Response to polarization and weak topology in Chern insulators
• Topologically distinct atomic insulators
• Reshaped Weyl fermionic dispersions driven by Coulomb interactions in MoTe2
• Emergent metallicity at the grain boundaries of higher-order topological insulators
• Grain-boundary topological superconductor
• Quantum spin Hall states in the lateral heteromonolayers of WTe2-MoTe2
• Hybrid symmetry class topological insulators
• Dispersive nodal fermions along grain boundaries in Floquet topological crystals
• Projected branes as platforms for crystalline, superconducting, and higher-order topological phases