Dresden 2026 – wissenschaftliches Programm

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FM: Fachverband Funktionsmaterialien

FM 22: Focus Session: Materials Discovery III – New materials and functionalities by general principles

FM 22.4: Vortrag

Freitag, 13. März 2026, 10:30–10:45, BEY/0138

Symmetry-Driven Transitions Between Flat Bands and Dirac Cones in Bilayer Kagome Lattices — •Taylan Gorkan — Bilkent University-UNAM

Flat bands (FBs) and Dirac cones represent two distinctive features of topological electronic systems, yet a unified mechanism enabling transitions between them has remained elusive to date. Here, we demonstrate a symmetry-governed and tunable transition from flat bands to Dirac cones in AB-stacked bilayer kagome lattices. This transition is mediated by the interplay between destructive quantum interference (DQI), C3 rotational symmetry, and spatial inversion symmetry. Strong interlayer coupling enhances DQI and stabilizes compact localized states that produce FBs, while weaker coupling allows C3 and inversion symmetries to dominate, giving rise to robust Dirac nodal points. Using a minimal tight-binding model, we map the continuous evolution of topological states-including type-II and type-III Dirac cones, spin-1 Dirac nodes, and partial flat bands-as a function of interlayer coupling. We further demonstrate this transition mechanism by examining an AB-stacked bilayer derived from the experimentally synthesized Nb3TeCl7 structure. In particular, first-principles calculations on bilayer Nb3TeCl7 reveal that vertical strain/pressure modulates interlayer interactions, enabling the entire FB-Dirac cones transition sequence. These findings establish a realistic novel pathway for gaining further insights into flat-band physics and engineering tunable topological phases in two-dimensional materials.

Keywords: Kagome; Flat bands; Dirac Cones; DFT