Cooling and heat transport in low dimensional phonon systems, superconductors and silicon
Muhonen, Juha (2012) Cooling and heat transport in low dimensional phonon systems, superconductors and silicon. PhD thesis, University of Warwick.
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Temperatures below 0.1 kelvin can be nowadays routinely attained. The
methods for achieving these temperatures rely on either mixing the rare
and expensive isotope of helium with the more common isotope (dilution
refrigerator) or on adiabatic demagnetisation of paramagnetic salt (ADR).
Although both of these methods are mature, they still remain complicated
enough to limit the usage only to specialized laboratories. The research
done in this thesis revolves around a promising alternative to these techniques;
using normal metal - insulator - superconductor (NIS) junctions.
One of the defining properties of a superconductor is a gap in its electronic
density of states. This gap enables it to act as an energy filter
for electrons. Because of this property, when a proper bias voltage is applied
over a NIS junction the normal metal part will cool down as current
passes the junction. The cooling properties of NIS junctions were demonstrated
almost two decades ago with cooling powers of the order of one
picowatt. At present cooling powers of few hundreds of picowatts have
This thesis describes research on three areas related to NIS junctions.
Firstly we use NIS junctions to cool low dimensional lattice systems, both
1D and 2D. The cooling of a 1D lattice (beam) is interesting for fundamental
research. The 2D lattice cooling (membrane) is aimed at bringing NIS
devices closer to more widespread use. An electronically cooled membrane
would offer a platform on which applications, such as radiation detectors
or superconducting electronics, could be integrated.
Secondly we focus on the limitations of NIS cooling. In all cooling, one
of the main problems is the dissipation of the extracted heat. As the other
side of the junction (normal metal) is cooled, the other side (superconductor)
is heated with many times larger power. This heat can then weaken
the superconducting properties and heat up the phonon system around
the junction. These effects act to counter the cooling effect and have been
one of the main obstacles in scaling up the cooling power of NIS devices.
We study these effects both numerically and experimentally.
Thirdly, we study the cooling of silicon with superconducting tunnel
junctions. In these superconductor - semiconductor structures the normal
metal in a NIS structure is replaced with highly doped silicon. Specifically
we study the effects of induced lattice strain to the electron-phonon
coupling in silicon and hence to the cooling properties of these structures.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QC Physics|
|Library of Congress Subject Headings (LCSH):||Cooling, Superconductors|
|Institution:||University of Warwick|
|Theses Department:||Department of Physics|
|Supervisor(s)/Advisor:||Pekola, Jukka, 1958- ; Kaivola, Matti ; Leadley, David|
|Sponsors:||Engineering and Physical Sciences Research Council (EPSRC)|
Publications not reproduced for copyright reasons
|Extent:||110, 23 leaves : ill., charts|
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