Jeonbuk National University (JBNU) Professor Jin Kyung-hwan (Department of Physics; G-Lamp Materials and Energy Basic Science Research Institute) research team, through an international collaborative study, has for the first time in the world observed a new quantum bound state induced by impurities in an exciton condensate.

This achievement was published online in Nature Nanotechnology (IF 37.5; JCR top 1.4%), the leading international journal in the field of nanoscience. The paper is titled “Defect-bound states of exciton condensate: a Yu-Shiba-Rusinov-state analogue.”

The research team examined, at the atomic scale, what happens when a very small impurity is introduced into an exciton condensate, a special quantum state formed when electrons and holes pair within a material. They found that the electron–hole pairing is locally disturbed around the impurity, producing a distinctive state that traps electrons like a tiny “quantum trap.”

Until now, it has been well known in superconductors that magnetic impurities disrupting electron-pairing give rise to peculiar quantum states inside the energy gap, known as Yu–Shiba–Rusinov (YSR) states. However, whether a similar phenomenon actually appears in exciton condensates, where electrons and holes are paired, had been predicted theoretically but never experimentally confirmed.

The team studied the layered material tantalum–palladium–tellurium (Ta₂Pd₃Te₅), which exhibits excitonic insulating behavior below room temperature. Using scanning tunneling microscopy and spectroscopy to observe atoms one by one, they captured a pair of distinct quantum bound states appearing inside the energy gap around a particular palladium (Pd) defect. Theoretical analysis further identified a mechanism in which a local charge dipole formed at the defect perturbs the exciton order, giving rise to these bound states.

The core significance of this discovery is that impurities can be used not merely as “disturbances” but as fine probes that read out the properties of otherwise invisible quantum condensates. This opens new possibilities for future low-power electronic and information-processing devices and high-performance optoelectronic and quantum information devices. In particular, because exciton condensates exploit electron–hole pairing, they could form the basis of new information-processing schemes that operate with lower energy consumption than conventional electronic devices. At present, however, this is a fundamental research result aimed at understanding and controlling the principles of next-generation quantum devices that could operate near room temperature, rather than a commercialization-ready technology.

Professor Jin Kyung-hwan said, “This study represents the first direct observation in an exciton condensate of a many-body quantum phenomenon corresponding to the well-known YSR state in superconductors. It is significant because it provides a new tool to precisely control and measure the microscopic quantum properties of high-temperature exciton condensates that persist up to near-room temperature.” He added, “We plan to extend applied research toward ultra-fast quantum information devices with low energy loss and interferometric optoelectronic devices.”

The research was carried out as an international collaboration involving JBNU, the Institute for Basic Science (IBS) Atomic Control Low-Dimensional Electron Systems Research Group, POSTECH, and the University at Buffalo. It was supported by the Ministry of Science and ICT and the National Research Foundation of Korea’s University Basic Research Institute Support Program (G-LAMP), among others.