no colloquium
Prof. Sergei Kravchenko
Northeastern University
Title: Metal-insulator transition and possible ferromagnetic instability in
2D
Abstract:
For nearly 20 years, it had been the prevailing view that there could be
no metallic state or metal-insulator transition (MIT) in two-dimensional
electron systems in zero magnetic field. However, in the last few
years, unusual behavior suggestive of such a transition has been
reported in a variety of strongly-correlated two-dimensional electron
systems. Although the physics behind these observations is not yet
understood, it has recently become evident that the interactions between
electrons are playing the key role. Recent observation of sharply
increasing spin susceptibility in the immediate vicinity of the MIT
suggests that the transition may be related to ferromagnetic
instability. I will review the main experimental results and suggested
explanations of these phenomena.
Prof. Peter W. Stephens
SUNY Stony Brook
Title: Malaria, Monte Carlo, and Synchrotron Radiation
Abstract:
The discovery of x-rays was one of the defining events of the
explosive growth of physics in the 20th century. There has been
a renaissance of x-ray technique in the last twenty or so years
based on the advent and promulgation of synchrotron sources.
I will talk about one family of modern applications of x-ray
diffraction; some tricky problems in determining the atomic
structure of matter. The central conceit of solid state physics
is that structure determines properties. Besides the kinds
of problems that one normally associates with solid state
physics (e.g., superconductivity in Fullerene materials),
we can make some unexpected contributions to biology and
medicine (e.g., how do anti-malarial drugs work, what can
we do about drug-resistant strains of malaria, and some
niche problems in protein structures).
Dr. Susan Ginsberg '94
American Physical Society
Title: From Lewis and Clark to Nanotechnology: How science policy REALLY works
Abstract:
America's science policy is determined by the President and the Congress
of the United States. At least that's what the civic textbooks would have us
believe. In reality, decisions about science budgets and research priorities
are affected by historical precedent, current events, and voters' opinions,
not to mention lobbyists and advocacy groups. Come learn about
the evolution of science policy, the current state of science budgets, and
how you can make a difference in the process.
Susan Ginsberg is currently as Senior Science Policy Fellow at the American Physical Society in Washington D.C. She has worked on Capitol Hill as a science policy expert and holds a bachelor's degree in geology from Amherst College, and a Masters in geophysics and a PhD in materials science engineering from the University of Minnesota.
no colloquium
cancelled
Dr. Charles Bennett
Five College Distinguished Speaker
Institution
Title: Information is Quantum
Abstract:
The information in a single photon or electron, somewhat like the
information in a dream, cannot be observed without disturbing it.
Our understanding of this delicate kind of information has increased
greatly over the last few years, leading to a deeper understanding of
other more familiar forms of information, and of natural processes in
general.
Dr. David Smith '95
MIT
Title: The hierarchy problem and physics beyond the Standard Model
Prof. Jeff Urbach '85
Georgetown University
Title: Shaking as Baking
Abstract:
I will discuss an experimental investigation of the dynamics of a
layer of about 15,000 uniform metallic spheres on a smooth horizontal
plate that is oscillating vertically. This system provides a simple
but striking demonstration of some of the unusual phenomena associated
with excited granular media (e.g. shaken sand). The energy input from
the plate vibrations causes the spheres to collide chaotically, much
like the molecules in a gas. In one regime, some of the spheres
'collapse', forming a stable, motionless crystalline island surrounded
by a coexisting gas. Other phase transitions are observed, closely
analogous to transitions seen in equilibrium thermodynamics. In
equilibrium, however, there is no energy flow, while the granular
'gas' requires continual energy input from the shaker, which is
eventually converted to heat through dissipative collisions. This
process leads to some remarkable non-equilibrium effects, including
non-Maxwellian velocity distributions and velocity
correlations that violate the molecular chaos assumption.
Dr. Kevin Mertes
CCNY
Title: Quantum Tunneling of Magnetism in the Single Molecule Magnet, Mn12-acetate
Abstract:
The mechanisms which drive the quantum tunneling of magnetism in the single
molecule magnet, Mn12-acetate have remain a mystery since the effect was first
discovered by J. Friedman et al. in 1995. Recent detailed magnetic measurements
of the crystalline form of Mn12 have brought us closer to fully understanding
the
tunneling phenomenon.
The central magnetic core of Mn12 consists of a group of ions strongly coupled
by
exchange interaction resulting in a large S=10 spin system. The structure of
the
molecule also produces strong anisotropy so that the spin of each molecule
prefers
to point either parallel or anti-parallel to the crystal's c-axis with a large
potential barrier separating the two orientations. When an external magnetic field is
applied
along the c-axis, a certain fraction of the molecules tunnel from one side of
the
potential barrier to the other whenever energy levels come into resonance. This
results in a set of steps in the magnetization curves.
The position of the steps have been successfully described by the effective
spin
Hamiltonian. However, the heights of the steps have required unphysically large
values of the symmetry breaking terms and have an unexpected dependence on the
field sweep rate. Detailed measurements indicate that this puzzling behavior
can
be explained in terms of a distribution of symmetry breaking terms.
Prof. Mark Tuominen
UMass
Title: Arrays of nanoscale magnets and superconductors made by guided
self-assembly
Abstract:
Nanotechnology is a rapidly developing research area. Many future
applications require ultrasmall elements configured into system
architectures that provide new functionalities. The progress toward
such goals involves a considerable amount of innovation and experiments
to understand the fascinating physics of nanoscale systems. This talk
will present an example of such work: the physics of arrays of magnetic
or
superconducting nanowires made by new nanofabrication techniques.
Prof. Mark P. Silverman
Trinity College
Title: Through a Fog Brightly: A Penetrating Look at Scattered Light
Abstract:
The need to see through turbid media--media rendered virtually
opaque by light scattering from suspended small particles--is frequently
encountered in science, technology, and medicine. Selective detection of
phase-modulated polarised light provides a way to penetrate this "fog" and
reveal (a) the presence and surface features of embedded objects invisible
to ordinary viewing, and (b) manifestations of left-right (chiral)
asymmetry in molecules of the host medium. Molecular chirality is the
chemical hallmark of terrestrial life.
Prof. Barbara L. Whitten
Colorado College
Title: TBA
Abstract:
TBA
NO TALK
Abstract:
TBA
Abstract:
TBA