Biomedical Engineering Reference
In-Depth Information
2.5.2 Metallic region
In the metallic region the resistivity has been found to be quite well
described by
CT
2
DT
n
rð
T
Þ¼r
0
þ
þ
½
2
:
7
where C is the electron-electron scattering coefficient and D is the electron-
phonon or electron-magnon scattering coefficient. The value of n has been
predicted to be 5 for electron-phonon scattering while it has a value of 4.5
for electron-magnon scattering.
2.6
Spin-dependent single-electron tunneling
phenomena
Scientific researchers are continuously searching for new technological tools
to comprehend and manipulate the basic elements available in nature. They
develop experiments and theories that can seem at first sight highly abstract,
virtually useless and far from meaning anything to our society. Strikingly, it
is precisely this attitude of exploring the 'extremes of what is possible' that
has induced the most significant technological breakthroughs to impact our
society. One important example is the discovery of a means to record the
magnetic properties of atomic nuclei, which is now widely applied as an
imaging tool in hospitals. Rapid developments in the computer industry are
based on the invention of the transistor, which was a result of fundamental
interest in the nature of electrons at the interface between a metal and a
semiconductor. Finally, the boost in data storage of the last decade, induced
by the discovery of a phenomenon called giant magnetoresistance, was
based on research on magnetic layers only one nanometer thick.
These developments have relied heavily on knowledge about the most
fundamental laws of physics, called quantum mechanics. Quantum
mechanics predicts how electrons move in materials, what processes lead
to light emission and the sources of magnetism. At this small scale, the laws
of nature exhibit some peculiar properties that contradict usual physical
laws. Examples of this are particles that start behaving like waves and the
striking manifestation of superposition states, where a particle can exist at
multiple positions at the same time. Most surprisingly of all, it has been
found that two particles can share a connection, called entanglement, even if
they are separated by a very long distance.
It is now possible to control these phenomena in very small systems like a
single atom or electron. This level of control makes it possible to address
important questions about the stability of quantum superpositions and
entangled states and how these are affected by measurements or interactions
