The
Condensed Matter and Biophysics Group
Emeritus
Faculty: Jones - Tomasch
Condensed
matter (CM) research at Notre Dame encompasses topics of research
ranging from “hard” CM problems such as semiconductor or superconductor
systems to “soft” CM problems such as studies of multicellular aggregates
or the application of network theory to biological systems. The
topics studied are described below:
Physics
on the Nanoscale
Single-electron
charging effects and related phenomena are explored to probe the
basic physics of few-atom clusters, fullerenes and other exotic
systems comprised of only a few atoms. The growth and self assembly
of quantum dots, quantum wires, and heterostructures in semiconductor
systems is also studied extensively. Work on heterostructures includes
the development of blue-light semiconducting lasers. Self-organized
quantum dots and other nanophase systems are grown and characterized
using optical, magnetic, transport, and x-ray techniques. Facilities
include a dual-chamber molecular beam epitaxy machine, extensive
facilities for optical and magneto-optical studies of nanoscale
systems with micrometer-scale and sub-micrometer-scale (near field)
resolution, and instrumentation for the study of electrical transport
and magnetic properties.
Semiconductor
Physics and Magnetism
Thin-film
II-VI, III-V and other semiconductor samples are prepared by molecular
beam epitaxy. III-V semiconductors which incorporate Mn ions in
the lattice are ferromagnets and are expected to play a key role
in future “spintronic” devices. These, as well as other magnetic
samples, are studied by a variety of experimental techniques including
laser magneto-spectroscopy, x-ray and neutron scattering, and electron
transport. Facilities include extensive capabilities for the study
of electrical properties, magnetization, and state of the art apparatus
for the study of magnetic resonance. In addition, magnetic properties
of solids are studied by neutron scattering, carried out off campus
at the National Institute for Standards and Technology and at the
University of Missouri Research Reactor Center (MURR).
Structural
Studies
X-ray
scattering and X-ray absorption fine structure (XAFS) are used to
study the surfaces and internal interfaces of solids and liquids,
phase transformations and ordering phenomena in condensed-matter
systems. Examples of recent studies atomic-scale structure of “highly
correlated” magnetic materials, interfaces and structure of magnetic
semiconductors, the structure of complex nanophase materials, the
structure of metalloproteins, and environmental systems on the molecular
scale. Because of the unique advantages of synchrotron radiation,
these experiments are conducted at national facilities located at
the Advanced Photon Source, Argonne National Laboratory, where Notre
Dame is a major participant.
Superconductivity
and Vortices
High-temperature
superconductors are studied from the perspective of microwave absorption
and other techniques with a view to probing fundamental mechanisms.
These include investigations of the response of high-temperature
superconductor thin-film systems to ultrashort duration, far-infrared
light to evaluate potential applications for and the intrinsic electronic
properties of these novel materials. New materials are synthesized
using the traveling solvent float zone (TSFZ) technique in a mirror
furnace-based system.
In
a separate effort, new superconducting systems based on dilute-doped
elemental superconductors are being developed for micro-refrigerators
and transition-edge x-ray sensors for space missions. Facilities
include thermal evaporation and multi-source sputtering systems,
a cold head for electro-optic studies down to 25K, a SQUID voltmeter,
a 10 T superconducting magnet, low-temperature equipment for work
to 1 K, and a clean room for contact lithography. A fiber optic
link to the lab of a collaborating atomic physicist permits the
piping of modulated laser light to these experiments. Collaborations
with NIST, Boulder, provide access to an extensive class-100 clean-room,
adiabatic refrigeration to 60 mK, and magneto-optic facilities.
Scanning
tunneling microscopy and spectroscopy (STM/STS) are used to image
vortices induced by an applied magnetic field and probe their spectroscopic
properties. These measurements are complemented with studies of
the vortex lattice structure using small-angle neutron scattering
(SANS). Combined, the two techniques allows a study of how the superconducting
gap and the vortex lattice symmetry and orientation evolves as a
function of temperature and field. On-site facilities include a
low-temperature, ultra-high vacuum STM (under construction) while
the neutron scattering studies are largely conducted at the Institut
Laue-Langevin, Grenoble, France.
Theoretical
Condensed Matter Physics
Notre
Dame theoretical condensed matter physicists study superconductors,
semiconductors, soft matter, and properties of networks.
In
one theoretical effort in superconductivity, finite temperature
field-theory techniques are used to study two-dimensional antiferromagnets.
Also studied are highly-correlated electronic systems, including
disordered and frustrated ferromagnets, such as magnetic semiconductors,
high temperature superconductors, the novel superconducting compound,
MgB 2 , and mesoscopic superconductivity. In semiconductors, an
active collaboration exists between theorists and experimentalists
studying mesoscopic and nanoscopic physics. In particular, Zeeman-induced
nanoscale localization of spin-polarized carriers in magnetic semiconductor-permalloy
hybrids is studied. In another project, Monte Carlo simulations
are used to study the microstructure of strained semiconductor alloys
and compounds.
Finally,
the tools of statistical mechanics are applied to understanding
real networks, including metabolic and genetic networks, social
networks, the Internet, and the World Wide Web. A special focus
is towards understanding the implications of the scale-free characteristics
of real networks, a concept developed at Notre Dame.
Biophysics
The
department hosts an active program In biophysics, focusing on modeling
the structure and development of various biological systems. A strong
focus is on understanding the topological properties of cellular
networks--the networks formed by the Interactions between metabolites,
genes and proteins, modeling both their structure and dynamical
behavior. Using techniques from statistical mechanics, models of
“convergent extension” cell rearrangements have been developed as
a way to understand one step in embryonic development. At a higher
level, multicellular aggregates, such as embryonic and mature tissues,
are modeled. These systems often share the properties of “excitable
media” and “soft matter,” familiar to modern condensed matter physics
and dynamical systems theory. Biological research is carried out
in collaboration with other groups on the campus, involving faculty
from biochemistry and biology, under the coordination of the Center
for Biocomplexity.
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