In collaboration with researchers from Spain and the United States, our colleagues Tonica Valla and Vesna Milšić Trontl contributed to the discovery of the influence of magnetic moiré potential on topological surface states that leads to correlated topological phases. The results have been published in the prestigious journal ACS Nano.
Topological insulators are a special class of materials that behave as electrical insulators in their bulk but exhibit highly conductive surfaces. On these surfaces, electrons act as Dirac fermions, whose spin and momentum are locked. This unique property makes them highly promising for applications in spintronics and quantum computing.
When topological insulators are placed in proximity to magnetic or superconducting materials, additional quantum phenomena can emerge – such as quantum anomalous Hall effect or Majorana fermions. Even richer phenomena are expected in moiré superlattices, patterns that form when two layers are overlaid with a different lattice constants or with a slight twist of layers, a concept well-known from graphene research. In such systems, electronic correlations can be greatly enhanced – a task that was until now notoriously difficiult to achieve in topological materials, and experimental evidence of these effects has been lacking.
In this study, the moiré superlattice was created by growing two-dimensional magnetic van der Waals insulators FeX₂ (X = Cl or Br) on the surface of the topological insulator Bi₂Se₃. Using scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), the researchers explored the electronic properties of the resulting moiré structure and demonstrated that its characteristics can be tuned by the choice of the FeX₂ film.
ARPES experiments revealed replicated Dirac cones, and particular attention was given to their crossing points, which in the FeBr₂/Bi₂Se₃ system occur below the Fermi level. We identifiy the signatures of small gaps at the intersections around the M̅i points that we attribute to the moiré interaction.. These findings point to a specific type of magnetic moiré potential that breaks time-reversal symmetry at those points but not at the Γ̅ point.
This work presents a compelling scenario for correlated topological phases induced by a magnetic moiré superlattice, potentially leading to topological superconductivity, phases with high Chern numbers, and exotic non-collinear magnetic textures.
Full paper is available on the link: doi/10.1021/acsnano.5c10193
We identify the signatures of small gaps at the intersections around the M̅i points that we attribute to the moiré interaction.