New tool probes quantum properties of exciton condensates

Researchers have, for the first time, visualized in-gap electronic states bound to impurities within an exciton condensate phase of the van der Waals crystal Ta₂Pd₃Te₅ at 4.4 K, utilizing scanning tunnelling microscopy and spectroscopy. This observation establishes an analogue to the Yu-Shiba-Rusinov state, typically seen in superconductors, but within this distinct quantum condensate. The energies of these impurity-bound states correlate with the excitonic band gap, a property tunable by local strain and carrier injection, potentially allowing control of quantum properties even at room temperature. These findings introduce a microscopic tool to probe and control quantum properties in exciton condensates. The van der Waals crystal Ta₂Pd₃Te₅ exhibits a structural arrangement of alternating one-dimensional chains of tantalum and palladium, sandwiched between tellurium layers; this specific layering is critical to its observed properties. Unit cells of the material contain two Ta₂Pd₃Te₅ layers, with tellurium atoms forming alternating dimer and trimer chains along the c-axis, a configuration clearly visualized through scanning tunneling microscopy and corroborated by density functional theory calculations. These calculations also detail the electronic band structure,…