Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU
Dr Dumitru Calugaru, Rudolf Peierls Centre for Theoretical Physics, University of Oxford Department of Physics, Princeton University
Prof Amalia Coldea
Abstract
Topologically trivial insulators are classified into two primary categories: unobstructed and obstructed atomic insulators. While both types can be described by exponentially localized Wannier orbitals, a defining feature of obstructed atomic insulators is that the centers of charge of these orbitals are positioned at empty sites within the unit cell, rather than on atoms. Despite extensive theoretical predictions, the unambiguous quantitative experimental identification of an obstructed atomic phase has remained elusive. In this work, we present the first direct quantitative experimental evidence of such a phase in 1H-NbSe2. We develop a novel method to extract the inter-orbital correlation functions from the local spectral function probed by scanning tunneling microscopy (STM), leveraging the orbital wave functions obtained from ab initio calculations. Applying this technique to STM images, we determine the inter-orbital correlation functions for the atomic band of 1H-NbSe2 that crosses the Fermi level. Our results show that this band realizes an optimally compact obstructed atomic phase, providing the unambiguous experimental identification of such a phase. Our approach of deconvolving the STM signal using ab initio orbital wave functions is broadly applicable to other material platforms, offering a powerful tool for exploring other electronic phases.