New evidence of an anomalous phase of matter brings energy-efficient technologies closer
From: The University of Cambridge Department
of Physics Cavendish Laboratory
July 14, 2021 -- Researchers have found evidence for an anomalous phase of matter that was
predicted to exist in the 1960s. Harnessing its properties could pave the way
to new technologies able to share information without energy losses. These results are
reported in the journal Science Advances.
While investigating a quantum material,
the researchers from the University of Cambridge who led the study observed the
presence of unexpectedly fast waves of energy rippling through the material
when they exposed it to short and intense laser pulses. They were able to make
these observations by using a microscopic speed camera that can track small and
very fast movement on a scale that is challenging with many other techniques.
This technique probes the material with two light pulses: the first one
disturbs it and creates waves – or oscillations - propagating outward in
concentric circles, in the same way as dropping a rock into a pond; the second
light pulse takes a snapshot of these waves at various times. Put together,
these images allowed them to look at how these waves behave, and to understand
their ‘speed limit.’
“At room temperature, these waves move
at a hundredth of the speed of light, much faster than we would expect in a
normal material. But when we go to higher temperatures, it is as if the pond
has frozen,” explained first author Hope Bretscher, who carried out this
research at Cambridge’s Cavendish Laboratory. “We don’t see these waves moving
away from the rock at all. We spent a long time searching for why such bizarre
behaviour could occur.”
The only explanation that seemed to fit
all the experimental observations was that the material hosts, at room
temperature, an “excitonic insulator” phase of matter, which while
theoretically predicted, had eluded detection for decades.
“In an excitonic insulator, the observed
waves of energy are supported by charge neutral particles that can move at
electron-like velocities. Importantly, these particles could transport
information without being hindered by the dissipation mechanisms that, in most
common materials, affect charged particles like electrons,” said Dr Akshay Rao
from the Cavendish Laboratory, who led the research. “This property could
provide a simpler route toward room-temperature, energy-saving computation than
that of superconductivity.”
The Cambridge team then worked with
theorists around the world to develop a model about how this excitonic
insulating phase exists, and why these waves behave in this way.
“Theorists predicted the existence of
this anomalous phase decades ago, but the experimental challenges to see
evidence of this has meant that only now we are able to apply previously
developed frameworks to provide a better picture of how it behaves in a real
material,” commented Yuta Murakami, from the Tokyo Institute of Technology, who
collaborated on the study.
“The dissipationless energy transfer
challenges our current understanding of transport in quantum materials and
opens theorists' imaginations to new ways for their future manipulation,” said
collaborator Denis Golež, from the Jozef Stefan Institute and University of
Ljubljana.
“This work puts us a step closer toward
achieving some incredibly energy-efficient applications that can harness this
property, including in computers.” concluded Dr Rao.
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