New Paper Online: Visualizing the Localized Electrons of a Kagome Flat Band
We are excited to share the first piece of work that comes out of our home-built MBE-STM system. In this work, we used spectroscopic mapping with the STM to visualise the real space localisation of the non-trivial Wannier states of a Kagome Flat Band. Kagome metals host a lattice-symmetry induced flat band in their electronic structure. Because the kinetic energy of electrons occupying these flat bands is quenched, quantum-mechanical interactions can emerge as the leading energy scale. Hence, the kagome materials are an attractive venue to explore the possible emergence of strongy-correlated many-body states that are predicted to exist in their flat bands.
Key to realize these proposals is to demonstrate the real space localization of kagome flat band electrons. In particular, the extent to which the often more complex lattice structure and orbital composition of realistic materials counteract the localizing effect of destructive interference, described by the 2D kagome lattice model, is hitherto unknown. We used STM to visualize the non-trivial Wannier states of a kagome flat band at the surface of CoSn, a kagome metal. We find that the local density of states associated with the flat bands of CoSn is localized at the center of the kagome lattice, consistent with theoretical expectations for their corresponding Wannier states. Our results show that these states exhibit an extremely small localization length of two to three angstroms concomitant with a strongly renormalized quasiparticle velocity, which is comparable to that of moiré superlattices. Hence, interaction effects in the flat bands of CoSn could be much more significant than previously thought. Our findings provide fundamental insight into the electronic properties of kagome metals and are a key step for future research on emergent many-body states in transition metal based kagome materials.
We currently work on realising a partially-filled Kagome Flat Band in CoSn by carrying out modulation and stoichiometric doping with our MBE system. Stay tuned for updates on this exciting subject!
In the meanwhile, we invite you to read our preprint if you want to learn more: Link to Preprint