Korean researchers achieve nanometer-scale control of exciton condensate, raising hopes for ultra-low-power devices

South Korean researchers have opened a path to precisely controlling an exciton condensate — a next-generation quantum material capable of dramatically reducing energy losses from electrical resistance and heat — at the nanometer scale. The breakthrough is expected to aid the development of ultra-low-power information devices at a time when AI and high-performance computing are driving a sharp rise in electricity consumption.

The Institute for Basic Science announced Thursday that a research team led by Yeom Han-woong, director of the Center for Artificial Low Dimensional Electronic Systems and a physics professor at Pohang University of Science and Technology, had for the first time in the world observed a new electronic state forming around atomic defects inside an exciton condensate and successfully controlled it at the nanometer scale.

An exciton is a bound pair formed when a negatively charged electron and a positively charged "hole" — the vacancy left behind when an electron departs — attract each other. The pair behaves as a single, electrically neutral particle.

Exciton condensation is the phenomenon in which a large number of excitons, rather than moving independently, collectively settle into a single, ordered quantum state. Because an exciton condensate can transmit information in a superfluid state — unlike conventional electron-based methods — it has attracted attention as a candidate for future information devices that could sharply cut energy losses.

In practice, however, realizing exciton condensation in solid materials has been extremely rare. The research team focused on the layered material Ta₂Pd₃Te₅, whose properties are preserved even at room temperature, and analyzed how atomic defects inside the material affect the exciton condensate.

Observations made with a scanning tunneling microscope revealed a pair of electronic states around certain atomic defects that had not previously been seen. Although each defect itself was no larger than a single atom, the newly formed electronic states spread roughly 5 to 6 nanometers into the surrounding area.

Through experiments and theoretical calculations, the team established that this phenomenon was not simply a case of electrons becoming trapped at defects, but rather a new quantum state created by the interaction between the atomic defects and the exciton condensate.

Most notably, the team made the world's first direct observation of a defect quantum state in an exciton condensate analogous to the Yu-Shiba-Rusinov (YSR) state seen in superconductors — a state whose existence had until now been predicted only in theory.

The research team also succeeded in directly manipulating the quantum state. When they applied localized strain to the material to weaken the exciton condensation, the defect electronic state disappeared along with it. When they used the scanning tunneling microscope tip to alter the local charge, both the energy gap representing the exciton condensation and the defect electronic state changed simultaneously.

This demonstrates that the exciton condensation state can be precisely controlled within a region of just a few nanometers. The team expects the finding to serve as an important foundational technology for realizing ultra-low-power electronic and optoelectronic devices based on excitons.

"We have proposed a new method for confirming and controlling the exciton condensation state at the atomic and nanometer scale," Yeom said. "We expect this to lay the groundwork for developing ultra-low-power future devices by advancing precision control technology."

The findings were published Thursday in the international journal Nature Nanotechnology.