Observation of Gapped Dirac Cones in a Two-Dimensional Su-Schrieffer-Heeger Lattice

TL;DR

This study demonstrates the presence of gapped Dirac cones in a 2D silicon lattice on silver, modeled by the SSH framework, revealing topological edge states and providing a new platform for exploring 2D topological physics.

Contribution

It provides the first material realization of a 2D SSH model with gapped Dirac cones in a silicon lattice, combining experimental and theoretical analysis.

Findings

Gapped Dirac cones observed at Brillouin zone corners.

Dirac bands described by a 2D SSH model with anisotropic polarization.

Presence of topological edge states in the silicon lattice.

Abstract

The Su-Schrieffer-Heeger (SSH) model in a two-dimensional rectangular lattice features gapless or gapped Dirac cones with topological edge states along specific peripheries. While such a simple model has been recently realized in photonic/acoustic lattices and electric circuits, its material realization in condensed matter systems is still lacking. Here, we study the atomic and electronic structure of a rectangular Si lattice on Ag(001) by angle-resolved photoemission spectroscopy and theoretical calculations. We demonstrate that the Si lattice hosts gapped Dirac cones at the Brillouin zone corners. Our tight-binding analysis reveals that the Dirac bands can be described by a 2D SSH model with anisotropic polarizations. The gap of the Dirac cone is driven by alternative hopping amplitudes in one direction and staggered potential energies in the other one and hosts topological edge states. Our results establish an ideal platform to explore the rich physical properties of the 2D SSH model.