Dresden 2026 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 74: Topological Insulators
TT 74.1: Talk
Thursday, March 12, 2026, 09:30–09:45, CHE/0091
Probing the Quantized Berry Phases of an Obstructed Atomic Band in 1H-NbSe2 Using Scanning Tunneling Microscopy — Dumitru Călugăru1,2, Yi Jiang3, Haojie Guo3, Sandra Sajan3, •Yongsong Wang3, Haoyu Hu1,3, Jiabin Yu1, B. Andrei Bernevig1,3, Fernando de Juan3, and Miguel M. Ugeda3 — 1Princeton University, Princeton, USA — 2University of Oxford, Oxford, United Kingdom — 3Donostia International Physics Center, San Sebastián, Spain
Topologically trivial insulators can host obstructed atomic phases, where the electronic charge is localized at symmetry positions that do not coincide with atomic sites. Despite intense theoretical interest, such phases have lacked quantitative experimental confirmation. Here we provide direct experimental evidence that the narrow band at the Fermi level of monolayer 1H-NbSe2 and TaSe2 realizes an optimally compact obstructed atomic phase by means of STM/STS (1). Bias-dependent constant-height conductance maps reveal a strong redistribution of spectral weight between inequivalent high-symmetry positions within the unit cell. We identify these positions experimentally by using substitutional transition-metal alloys and chalcogen vacancies as local markers. By deconvolving the STM images with orbital-resolved wave functions from ab-initio calculations, we reconstruct the short-range inter-orbital correlations and real-space charge distribution associated with the band. The resulting pattern is centered at non-atomic positions and is uniquely consistent with an obstructed atomic insulator.
[1] Calugaru et al., Nature Physics, in press(2025).
Keywords: 1H-NbSe2; LT-STM/STS; obstructed atomic insulators(OAI); molecular beam epitaxy