Transcript Quantum-Hall Physics - University of Warwick

The Physics Theory Group @ Warwick
www.warwick.ac.uk/go/theory
Diffusion Limited
Aggregation
Classical Physics
This sort of growth we study by
simulation and recently
analytic theory. It is what
makes snowflakes so varied,
but it is also why your
rechargeable batteries don’t
last.
Suppressing this sort of
pattern when you inject water
into an oil reservoir is a trillion
dollar industry.
Dynamical Fracture
What controls the roughness and
branching of crack propagation
patterns?
Experimentally based claims of
universal behaviour suggest we
should be able to understand this
from computer simulations
See the simulations on our
website!
Quantum Physics
Academic Staff
Prof Mike Allen
Quantum Chaos
Prof Robin Ball
The quantum mechanics of systems which are classically
chaotic has been an intense focus of interest in recent
years, particularly as experimental realisations as above
can now be taylor-made.
Dr Nick D'Ambrumenil
Dr John Dixon
Dr Boris Muzykantskii
Dr Mario Nicodemi
Dr Rudolf A Römer
Quantum-Hall Physics
Prof George Rowlands
Dr Ellak Somfai
Dr Marzena Szymanksa
Prof Julie Staunton
Pattern Formation in Granular Systems
Dr Matthew Turner
Measuring a voltage difference in a thin layer of
semiconductors allows us to observe quantum effects with
astonishing accuracy. The quantum-Hall effect is currently used
to define what we mean by the SI unit of “resistance”, it is
among the most precise measurement of nature constants
possible. At the heart of each measurement is the
observational fact that h/e2 is quantized.
The picture shows a model for the electronic structure in a
semiconductor.
Granular Systems which are shaken rather than in thermal motion can
develop unexpected patterns.
In both of the above the shaking is from side to side and the view from
above. The initially separated and initially mixed samples follow very
different paths to similar end states. Challenge: understand the overall
mechanism, timescales, and what so strongly selects the final state?
Meiosis (dynamics of
sex)
Meiosis is the specialized cell
division necessary for the
production of haploid gametes
from diploid nuclei. In a crucial
step, homologous (i.e. same
number) chromosomes pair up,
but how they recognize each other
and come together are still
mysterious.
We studied a Statistical
Mechanics Model for the
regulation of such processes.
Is DNA conducting?
Myosin Walkers
To keep cells alive tiny molecular machines are
needed to move cargo around. These can have
efficiencies that are comparable to the best
machines that engineers can build today but are
only a few nanometres across and have to live in
a very 'noisy' environment. They are highly
evolved structures that use chemical energy to
generate forces, and hence motion by exploiting
cyclic reaction pathways. We are interested in
understanding these theoretically, e.g. for twolegged 'walkers' (as shown) how is the rear leg
'told' when to detach and take a step forward ?
Our genetic information is stored in large
Deoxyribonucleicacid (DNA) molecules. Typically,
billions of bases form one DNA molecule in
mammals and base pairs are seperated by 0.34
billionth of a meter from each other. There is
evidence that hese large chains might be used as
nano-wires.
An issue of scientific concern is the exact way in
which DNA and other biomolecules such as proteins
signal one another in order to carry out the required
operations. Both to scientists and to the untrained
eye it seems fascinating how DNA-binding proteins
find their way across thousands of bases in a DNA
sequence and know exactly where to attach
themselves to, i.e. their target, which could be a
fragment as short as a few tens of bases. There is a
signalling method, speculated to involve electrons,
that guides processes like these.
Healthy DNA
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electron
Biological Physics
insulator
Bose-Einstein Condensation
After nearly a century of theoretical speculation, this is now
an experimental reality. The first demonstration was in
ultra-cold and ultra-dilute atoms, but above shows the
evidence for condensation of polariton excitations in a
solid. The nearer figures show occupation number as a
function of momentum, with a macroscopic peak emerging.
Our newest group member works on techniques to model
these systems.
Wavefunctions amidst Disorder
As material disorder gets stronger, the nature of particle wave functions
changes from extended to localised, and what was a metal becomes an
insulator.
This image illustrates the subtlety observed at the metal-insulator
transition.
Magnets and Nano-technology
The main theme running through most of this research is a description of
various properties of metallic materials via a careful account of their
electronic `glue' or structure. This requires `state of the art' computing
techniques and resources such as those available at the Centre for Scientific
Computing at the University of Warwick. We study theoretical metallic
magnetism in this way and also, with the same electronic basis, a theory for
the types of alloys that can form when two or more metallic elements are
combined. A strength of the work is that it is `first-principled' so that many
aspects can be tested in quantitative detail by a range of experimental
measurements.
Fermi Surface of
Copper
The key to understanding the
electronic properties of metals is
to view things in Momentum
Space – a three dimensional
Fourier Transform.
This image shows the states
occupied by electrons. The
greatest distortion from a sphere
happens when the states come
closest to the edge of the Brillouin
Zone.
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Broken DNA
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metal
Applications
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© RA Roemer 2005