Possible Excitonic Insulating Phase in Quantum-Confined Sb Nanoflakes

TL;DR

This study provides experimental evidence that quantum-confined Sb nanoflakes can host an excitonic insulator phase, characterized by a charge density wave without lattice distortion, driven by enhanced Coulomb interactions.

Contribution

First direct STM/STS evidence of excitonic insulator phase in elemental Sb nanoflakes due to quantum confinement effects.

Findings

Observation of charge density wave without lattice distortion

Detection of a gap near the Fermi surface induced by CDW

Identification of Sb nanoflake as an excitonic insulator

Abstract

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.