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New
Release -- Superconductor Week does not edit or endorse the following
news release:
Quantized Heat Conduction by Photons Observed
Helsiniki, Finland, November 9: In a recent experiment, to be published
in Nature on November 9, Dr Matthias Meschke and professor Jukka Pekola,
together with Dr Wiebke Guichard, a coworker from French CNRS, investigated heat
exchange between two small pieces of normal metal, connected to each other only
via superconducting leads. The results demonstrate that at very low temperatures
heat is transferred by electromagnetic radiation.
The PICO research group is a
part of the Low Temperature Laboratory at
Helsinki University of
Technology - TKK, Finland. The domain of interest of the PICO research group
is how heat is transported in nano- and micrometer sized devices on an ordinary
silicon chip at only 0.1 degrees above absolute zero.
The project is part of the
Future Electronics (TULE) Research Programme of the Academy of Finland.
Generally, even experts
consider that superconductors are ideal insulators as regards to usual heat
conduction. These new experimental results demonstrate that at very low
temperatures heat is transferred by electromagnetic radiation, much in analogy
to how light is propagated, along the superconductors, and furthermore these
observations show that the heat transfer rate cannot have an arbitrary value: it
is limited by what is called a quantum of thermal conductance. As is often the
case, this observation contradicts our experiences in daily life. Certainly, one
would not see this effect for instance while cooking an egg; it is just another
example of how physical laws are changing when quantum mechanics comes into
play.
These experiments are quite
demanding, as they have to measure the temperature of an extremely tiny piece of
a metal. Any usual thermometer would not do it, as it is simply far too big.
Again, only the quantum mechanics can provide a solution: nano-sized (about 100
nm in cross-section) probes make use of the quantum mechanical effect of
tunneling, that is penetration of particles through a classically forbidden
area. Electrical current due to tunneling probes the energy distribution, and
thus temperature, of the electrons in the metal. The experiment may have seemed
too easy, unless, in order to distinguish the signal from the background, the
researchers had to install an “in-situ” switch into the superconducting line:
this allowed them to alternatively either pass or reject the heat by
electromagnetic radiation through it.
The observation demonstrates a
very basic phenomenon, which has no immediate consequences for new products or
applications. Yet the observation helps us to understand the fundamental
transport mechanisms in nanoscale devices. This effect has implications for,
e.g., performance and design of ultra-sensitive radiation detectors in
astronomy, whose operation at very low temperature is largely dependent on weak
thermal coupling between the device and its environment.
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