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In general, I am interested in doing cryogenic imaging of
electrons in "highly-correlated electron" materials.
Some of the materials that interest me are:
- AlGaAs/GaAs low density 2DEG: By using Molecular Beam
Epitaxy, it is possible to grow gallium arsenide semiconductor wafers
where the electrons are confined to a very thin, high mobility channel
below the surface. This type of structure is called a 2-dimensional
electron gas (2DEG). The properties of strongly interacting two
dimensional electrons are not very well known: calculations that
include full many body interactions in two dimensions are very
difficult to do. At low electron densities, where electron
interactions become stronger, there exists the possibility that the
electrons may form some kind of an exotic (non-fermi liquid) many body
state.
- Organic Semiconductors: There have been recent
measurements where the fractional quantum hall effect (FQHE) was seen
in pentacene and tetracene single crystals at temperatures as high as
2 Kelvin. In conventional semiconductors, such as GaAs, temperatures
usually need to be 300 mK or lower to avoid having the many-body
interactions being washed out by thermal scattering. The fact that the
FQHE state persist to such a high temperature in these materials is an
indication of how strong the electron interactions are. It's all
pretty new, and a bit vague, but these have the possibility of
exhibiting some exciting physics.
- Niobium Diselenide: Niobium diselenide is a
conventional type II superconductor, with a transistion temperature of
about 7.2 Kelvin. The material also has a charge density wave (CDW)
transistion at 22 Kelvin. Aside from being an good STM calibration
sample, niobium diselenide is a widely used material for studying
vortices and vortex relaxations. The fact that it also has a CDW is an
indication that the electrons are pretty correlated. My knowledge of
the physics of NiSe2 is pretty superficial right now, and I want to
learn more about it.
- Superconducting Cuprates: This pretty much tops the
chart as far as exotic, correlated electrons. After 15 years, nobody
has be able to put together a completely convicing picture of why the
electrons in this material are able to retain their superconductivity
to such high temperatures, or even why they superconduct in the first
place. This one is hard, though, being plagued by serious problems
with the copper oxide materials themselves, and the politics
surrounding the field.
To study these materials we use two techniques: scanning
capacitance mode imaging (SCM), and scanning tunnelling imaging
(STM). These both use home-built scanning probe microscopes that we
operate at 20 mK (dilution fridge), 300 mk (3He system), and 1.5 -
300 K (flow cryostat).
Below are some links that have some more information about my
research.
- What do I want to do? I've outlined some ideas about what to
study with the new microscope in my research proposals report. Note that I
have not included my ideas about studying high temperature
superconductors in this. I am also interested in trying to do
tunnelling measurements on La2CuO_{4+y} materials. For some
background, see my term paper.
- What have I been doing for the last year? You can find a copy of
my May 2001 progress report here.
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