Defect-bound states of exciton condensate as an analogue of the Yu–Shiba–Rusinov state

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 bound states are predicted within quantum condensates of excitons, their existence has been elusive. Here we visualize in-gap electronic states bound to impurities inside an exciton condensate phase of a van der Waals crystal Ta2Pd3Te5 at 4.4 K, utilizing scanning tunnelling microscopy and spectroscopy. We find that the energies of in-gap states are 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 can be explained by charge dipoles associated with Pd atoms on Ta sites through a charge-exciton version of the YSR mechanism. Our findings introduce the analogue of YSR physics in exciton condensates and a microscopic tool to probe and control quantum properties in exciton condensates persisting up to room temperature. Impurities in a quantum exciton condensate create bound electronic states, as visualized in Ta2Pd3Te5, that are analogous to spin impurities in superconductors, enabling microscopic control of excitonic quantum matter.