The excitonic insulator is an electronically driven phase of matter that can occur in solids. Scientists are searching for ways to detect and stabilize this exotic order in candidate quantum materials because it could pave the way towards superfluid energy transport with no net charge (which is distinct from superconductivity). If realized, this phenomenon could lead to a new generation of devices where energy is transported at the nanoscale with high coherence and minimal dissipation.
However, spotting this phase in real solids has proven difficult so far. For the past two decades, it had been proposed that the quasi-two-dimensional solid Ta2NiSe5 may support an excitonic insulator phase above room temperature.
Above a critical temperature TC = 328 K, this material crystallizes in a layered structure that consists of parallel Ta and Ni chains. At TC, the system undergoes a semimetal-to-semiconductor transition, accompanied by a structural reorganization of the crystalline lattice. The scientific community has been engaged in an intense debate regarding whether this phase transition was induced by a purely electronic or a structural instability.
In a recently published study on PNAS, researchers in the U.S., Germany, and Japan probed the fundamental processes underpinning that transition via a joint experimental-theoretical approach.
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