Researchers have found evidence for the existence of an anomalous phase of matter, the existence of which was predicted in the 1960s. The use of its properties can pave the way for new technologies that can exchange information without wasting energy.
These results are reported in the journal Science Advances.
While exploring the quantum material, the University of Cambridge scientists who led the study noticed the presence of unexpectedly fast waves of energy passing through the material when they exposed it to short, intense laser pulses. They were able to make these observations using a microscopic high-speed camera that can track small and very fast movements at a scale that is difficult for many other methods. This technique explores the material with two pulses of light: the first perturbs it and creates waves - or vibrations - that propagate outward in concentric circles, similar to dropping a stone into a pond; a second light pulse takes a snapshot of these waves at different times. Taken together, these images allowed them to see how these waves behave and understand their "speed limit".
"At room temperature, these waves travel at a speed of one hundredth of the speed of light, which is much faster than we would expect in ordinary material. But when we move to higher temperatures, it feels like the pond is frozen," explained the first author by Hope Bretscher, who conducted research at Cambridge's Cavendish Laboratory. "We don't see these waves moving away from the stone at all. We've been looking for a long time why this strange behavior might be happening."
The only explanation that seemed to fit all experimental observations was that the material at room temperature contains an "exciton insulator" matter phase, which, although predicted theoretically, has not been detected for decades.
“In an exciton insulator, the observed energy waves are supported by charge-neutral particles that can move at speeds similar to those of electrons. Importantly, these particles can carry information without interference from the scattering mechanisms that in most common materials affect charged particles, such as electrons, "says Dr. Akshay Rao of the Cavendish Laboratory, who led the study. "This property could provide an easier path to energy-efficient computing at room temperature than superconductivity."
The Cambridge team then worked with theorists around the world to model how this excitonic insulating phase exists and why these waves behave this way.
"Theorists predicted the existence of this anomalous phase several decades ago, but experimental difficulties in obtaining evidence of this have led to the fact that only now can we apply the previously developed foundations to get a more complete picture of how it behaves in real material, "commented Yuta Murakami of the Tokyo Institute of Technology, who participated in the study.
"Dissipative energy transfer challenges our current understanding of transport in quantum materials and opens up new possibilities for theorists to manipulate them in the future," said author Denis Gole of the Jozef Stefan Institute and the University of Ljubljana.
"This work takes us one step closer to creating incredibly energy efficient applications that can take advantage of this property, including in computers," concluded Dr. Rao.