In the 1960s, it was proposed that in small indirect band-gap materials, excitons can spontaneously form because the density of carriers is too low to screen the attractive Coulomb interaction between electrons and holes. The result is a novel strongly interacting insulating phase known as an excitonic insulator. Here we employ scanning tunnelling microscopy (STM) and spectroscopy (STS) to show that the enhanced Coulomb interaction in quantum-confined elemental Sb nanoflakes drives the system to the excitonic insulator state. The unique feature of the excitonic insulator, a charge density wave (CDW) without periodic lattice distortion, is directly observed. Furthermore, STS shows a gap induced by the CDW near the Fermi surface. Our observations suggest that the Sb(110) nanoflake is an excitonic insulator.
@article{arxiv.2405.19566,
title = {Possible Excitonic Insulating Phase in Quantum-Confined Sb Nanoflakes},
author = {Zhi Li and Muhammad Nadeem and Zengji Yue and David Cortie and Michael Fuhrer and Xiaolin Wang},
journal= {arXiv preprint arXiv:2405.19566},
year = {2024}
}