Extraordinary transition at the edge of a correlated topological insulator

TL;DR

This paper investigates a boundary phase transition in a correlated topological insulator model, revealing a transition from a decoupled edge to an extraordinary-log phase with unique spectral signatures.

Contribution

It demonstrates a boundary phase transition in a Kane-Mele-Hubbard model at the XY critical point, highlighting the emergence of an extraordinary-log phase.

Findings

Boundary transition from helical Luttinger liquid to extraordinary-log phase

Logarithmic divergence of spin stiffness in the new phase

Distinct spectral features in different phases

Abstract

The interplay of topology and correlations defines a new playground to study boundary criticality in quantum systems. We employ large scale auxiliary field quantum Monte Carlo simulations to study a two-dimensional Kane-Mele-Hubbard model on the honeycomb lattice with zig-zag edges and the Hubbard U-term tuned to the three-dimensional XY bulk critical point. Upon varying the Hubbard-U term on the edge we observe a boundary phase transition from an ordinary phase with a helical Luttinger liquid edge decoupled from the critical bulk to an extraordinary-log phase characterized by a logarithmically diverging spin stiffness. We find that the spectral functions exhibit distinct features in the two phases giving potential experimental signatures.