Yu-Shiba-Rusinov bound states of exciton condensate

TL;DR

This study visualizes Yu-Shiba-Rusinov bound states within an exciton condensate in a van der Waals crystal, revealing their dependence on local strain and charge, and demonstrating a new way to probe quantum properties at room temperature.

Contribution

It provides the first direct visualization of YSR-like bound states in an exciton condensate and links their energies to local strain and charge, expanding understanding of impurity effects in quantum condensates.

Findings

In-gap states are observed inside the exciton condensate.

The energies of these states correlate with the excitonic band gap.

Charge dipoles from vacancies induce the in-gap states via a YSR mechanism.

Abstract

Quantum condensed states in solids often reveal their fundamental nature via interactions with impurities, as epitomized by Yu-Shiba-Rusinov (YSR) bound states at magnetic impurities in superconductors. Although analogous YSR bound states were predicted within quantum condensates of excitons several decades ago, their existence has been elusive. Here, we directly visualize in-gap electronic states bound to impurities inside an exciton condensate phase of a van der Waals crystal Ta2Pd3Te5, utilizing scanning tunneling microscopy and spectroscopy. We find that the energies of in-gap states are strongly correlated with the excitonic band gap, which is systematically tuned by local strain and carrier injection. Our theoretical analyses reveal that these in-gap states are induced by charge dipoles associated with Ta vacancies through a charge-exciton version of the YSR mechanism. Our findings establish both the YSR physics in exciton condensates and a novel microscopic tool to probe and control quantum properties in exciton condensates persisting up to room temperature.