Photo-electrons unveil topological transitions in graphene-like systems

TL;DR

This paper demonstrates that angle-resolved photoemission spectroscopy (ARPES) can detect topological transitions in graphene-like systems by measuring Berry curvature-related properties, providing a new experimental approach to study topological invariants.

Contribution

It introduces a novel spectroscopic method using ARPES with specific x-ray energies and polarization to measure Berry curvature and Chern number changes in topological materials.

Findings

ARPES can detect topological phase transitions in graphene.

Experimental evidence links dipolar matrix elements to topological invariants.

New routes for experimental topological studies in condensed matter systems.

Abstract

The topological structure of the wavefunctions of particles in periodic potentials is characterized by the Berry curvature $\Omega_{kn}$ whose integral on the Brillouin zone is a topological invariant known as the Chern number. The bulk-boundary correspondence states that these numbers define the number of edge or surface topologically protected states. It is then of primary interest to find experimental techniques able to measure the Berry curvature. However, up to now, there are no spectroscopic experiments that proved to be capable to obtain information on $\Omega_{kn}$ to distinguish different topological structures of the $\it{bulk}$ wavefunctions of semiconducting materials. Based on experimental results of the dipolar matrix elements for graphene, here we show that ARPES experiments with the appropriate x-ray energies and polarization can unambiguously detect changes of the Chern numbers in dynamically driven graphene and graphene-like materials opening new routes towards the experimental study of topological properties of condensed matter systems.