Step-Edge Anomaly in Topological Metals

TL;DR

This paper predicts that step edges on 3D topological metals exhibit a robust, non-integer conductance fixed by the bulk topology, extending the concept of boundary states in topological matter.

Contribution

It introduces the concept of a non-integer, bulk-determined conductance at step edges in topological metals, supported by theoretical modeling and experimental relevance.

Findings

Step edges in topological metals have a conductance K e^2/h with non-integer K.

K is fixed by the bulk topology of the material.

Experimental observations show enhanced density of states at step edges.

Abstract

Bulk-boundary correspondence guarantees the presence of robust, anomalous states on the boundary of topological matter. The edges of a two-dimensional Chern insulator harbor one-dimensional chiral states, which have a conductance $n\, e^2/h$, where $n$ is an integer that is solely determined by the bulk. In this work we show that step edges on the surface of three-dimensional topological metals have a robust conductance $K\, e^2/h$, where $K$ is also fixed by the bulk and assumes non-integer values. We explain this prediction on the basis of the topology of gapless systems, exemplify it on a lattice model, and connect to recent experimental observations of enhanced density of states at step-edges in topological metals.