Download Fall 2004 Colloquium Series Physics Department University of Oregon 3:30 Thursdays, 100 Willamette

Fall 2004 Colloquium Series
Physics Department
University of Oregon
3:30 Thursdays, 100 Willamette
(Reception at 3:15 in the Atrium)
September 30
State of the Department
(Host:Nöckel)
Dave Soper
Special room: 110 Willamette
Special date:
Wednesday, October 6
From spin-wave to
artificial light in a spin
system
Abstract:
Xiao-Gang Wen
We study a frustrated spin
system. We show that our model
contains a string-net condensed
state that results in an artificial
light -- a photon-like collective
excitation. The string-net
condensed state represents a new
state of matter. The existence of
artificial light (as well as artificial
electron) in condensed matter
systems suggests that elementary
particles, such as light and
electron, may not be elementary.
They may be collective excitations
Department of Physics
MIT
of quantum order in our vacuum.
(Host: Nöckel)
October 7
Dr. Nu Xu
Lawrence Berkeley National Lab
The ‘Big Bang’ in the
Laboratory -- The physics
of high-energy nuclear
collisions
Abstract:
The purpose of high-energy
nuclear collisions is to study
matter at very high energy
density. Under extreme
conditions, one expects a phase
transition from normal nuclear
matter to partonic matter -- the
formation of a
Quark-Gluon-Plasma (QGP). Such
a state is believed to have existed
for a few microseconds after the
big bang. In a QGP, deconfined
quarks and gluons will be able to
move freely in a volume much
larger than that of a nucleon. The
Relativistic Heavy Ion Collider
(RHIC) started to operate in 2000.
A large amount of high quality
data has been collected by the
RHIC experiments. In this talk, I
will review the status of RHIC
physics and discuss where we
stand with respect to a QGP
discovery.
(Host: Hwa)
October 14
Constantine Yannouleas
School of Physics
Georgia Tech
Formation and properties
of Wigner crystallites in
semiconductor quantum
dots
Abstract:
The two-step method [1] of
symmetry breaking at the
unrestricted Hartree-Fock (UHF)
level and of subsequent
post-Hartree-Fock restoration of
the broken symmetries via
projection techniques is reviewed
for the case of two-dimensional
semiconductor quantum dots
(QD's; often referred to as
artificial atoms). The general
principles of the two-step method
can be traced to nuclear theory
[2] and quantum chemistry [3];
however, in the context of
condensed-matter nanophysics, it
constitutes a novel theoretical and
computational approach. I will
demonstrate that this method is
able to describe a wide variety of
strongly correlated phenomena in
QD's in both the zero and finite
magnetic-field (B) regimes. These
include [1]: (I) Formation and
rotation of rigid (B = 0) and
floppy (finite B) Wigner molecules
(also referred to as electron
molecules; in other fields of
physics, molecular behavior of
electrons has been studied in the
context of doubly-excited states
of two-electron natural atoms
[4]); (II) Chemical bonding,
dissociation, and spatial
entanglement in quantum dot
molecules, with potential
technological applications to
quantum logic gates [5]; (III)
Pinning and distortions of Wigner
crystallites due to defects or
impurities. At high magnetic
fields, the two-step method yields
analytic many-body wave
functions
(rotating-electron-molecule wave
functions [6]), which are an
alternative to the
composite-fermion and
Jastrow-Laughlin approaches. The
rotating-Wigner-molecule
approach provides [6] a new point
of view of the fractional quantum
Hall effect in QD's, with possible
implications for the
thermodynamic limit.
1. C. Yannouleas and U.
Landman, Phys. Rev. Lett.
82, 5325 (1999); J. Phys.:
Condens. Matter 14, L591
(2002); Int. J. Quantum
Chem. 90, 699 (2002);
Phys. Rev. B 68, 035325
(2003); Phys. Rev. B 69,
113306 (2004).
2. P. Ring and P. Schuck, The
Nuclear Many-Body Problem,
(Springer, New York, 1980),
Ch. 11
3. P.-O.Löwdin, Rev. Mod.
Phys. 34, 520 (1962).
4. See, e. g., M. E. Kellman
and D. R. Herrick, Phys.
Rev. A 22, 1536 (1980).
5. G. Burkard, D. Loss, and D.
P. DiVincenzo, Phys. Rev. B
59, 2070 (1999).
6. C. Yannouleas and U.
Landman, Phys. Rev. B 66,
115315 (2002); Phys. Rev.
B 68, 035326 (2003);
cond-mat/ 0401610.
(Host: Nöckel)
Special time: 4 pm
October 21
A Spectroscopist's View
on Magnetic Materials
Abstract:
Kai Starke
Department of Physics
Freie Universität Berlin
Germany
A major goal in magnetic
materials research is to tune
properties such as anisotropy,
exchange coupling strength, and
magnetization. There is an
emphasis on layered structures
and heteromagnetic interfaces
today, in which rare-earth
elements are important owing to
the coexistence of large localized
magnetic moments and weak
indirect exchange coupling.
Focussing on fundamental aspects
of magnetism on the nanoscale,
we have investigated the
competition between antiferroand ferromagnetic coupling at an
atomically sharp interface, using
the strong magnetization
dependence of optical transitions
that involve 4f electrons. We find
a noncollinear spin structure that
is stabilized by a lattice
reconstruction [1,2]. Moreover,
the individual magnetic hysteresis
loops of two ferromagnetic layers
[3,4] coupled by a diamagnetic
spacer layer give evidence that
temperature can be used to
reverse the coupling. Finally,
exploring the ultimate limits of
fast magnetization dynamics we
observe the excitation of coherent
3-THz phonons together with
parametrically driven magnons [5]
in a fs-laser pulse pump-probe
scheme using SHG detection.
1. E. Arenholz et al., Phys.
Rev. Lett. 80, 2221 (1998)
2. K. Starke: Magnetic
Dichroism in Core-Level
Photoemission (Springer,
Berlin, 2000)
3. K. Starke et al., Phys. Rev.
Lett. 86, 3415 (2001)
4. J. E. Prieto et al., Phys.
Rev. B 68, 134453 (2003)
5. A. Melnikov et al., Phys.
Rev. Lett. 91, 227403
(2003)
(Host: Kevan)
October 28
Resonant light interaction
with nano-plasmonic
structures: field
enhancement, light
nano-guiding, and
left-handed media
Abstract:
With respect to their optical
properties, bulk metals and
dielectrics may be considered to
be two opposite extremes - one
"hating" (reflecting) the light,
another "loving" (transmitting or
absorbing) it. In this talk we will
describe the ways to combine the
metallic and dielectric
nano-structures to design new
types of optical media.
Viktor Podolskiy
Department of Physics
Oregon State University
Corvallis
We first introduce the
phenomenon of plasmon
resonance, and show how it can
be used for orders-of-magnitude
enhancement of local intensity,
enhanced nano-spectroscopy,
nano-sensing, and light guiding on
sub-wavelength scale
(nano-plasmonics). We will show
how the design of the system
affects the properties of plasmon
resonance from being narrow-band
in "periodic mesh" structures to
being broadband in disordered
(percolation) metal-dielectric
composites.
We will then consider the
perspectives of materials with
negative refractive index, often
associated with simultaneously
negative dielectric permittivity
and magnetic permeability and
the plausibility of their fabrication
at high (optical and infrared)
frequencies, where non-trivial
magnetic permeability is
hard-to-achieve. We will show
how the special type of plasmon
polariton resonance can be used to
excite magnetic moment at
optical frequencies, and describe
the ways to manipulate such a
resonance. Finally, we will
introduce a new type of
non-magnetic systems with
negative-n (left-handed) behavior
and propose several realizations of
such structures.
(Host: Nöckel)
November 4
What are the Limits of
Energy Focusing in
Sonoluminescence?
Abstract:
Seth Putterman
Department of Physics
UCLA
Sonoluminescence ['SL'] is an
amazing marker for the
extraordinary degree by which
ultrasonic energy can be focused
by a cavitating bubble of gas.
Local energy dissipation exceeds
Kirkhoffs law by 1015 and the
ambient acoustic energy density
concentrates by 12 orders of
magnitude to create picosecond
flashes of broadband ultraviolet
light. At the minimum bubble
radius where the contents have
been compressed to their van der
Waals hard core the acceleration
exceeds 1011g and a Mega-Bar
level shock wave is emitted into
the surrounding fluid. For single
bubbles driven at 30KHz SL is
nature's smallest blackbody. This
implies that the bubble's interior
is such a dense plasma that the
photon-matter mean free path is
shorter than the wavelength of
light, and suggests that SL
originates in an unusual state of
matter. Excitation of a vertical
column of fluid [~10Hz] so as to
create a water hammer leads to
the upscaling of SL so as to
generate flashes of light with over
1012 photons and peak powers
exceeding 1W. At 1MHz the
spectrum resembles
Bremstrahlung from a transparant
plasma with a temperature ~1MK.
At 10MHz the collapsed size of the
SL bubble approaches 10nm,
which raises the possibility that
the SL parameter space may
extend to the domain of quantum
mechanics. At 30MHz experiments
are under way to excite
sonoluminescence with sound
fields in excess of 3,000atm. The
strongest cavitation collapses may
be realized with M. Greenspans
ultrasonic resonators which can
reach sound fields in excess of 20
atm without cavitating. When
bubbles are seeded with an
external laser a massive
cavitation event ensues. Although
the SL mechanism and its robust
parameter space remain a
mystery it has already been put to
use as a surgical device. At 30KHz
it is used for internal lipectomy
and at 1MHz it is used for
externally assisted lipectomy.
(Host: Nöckel)
November 11
Dirk Bouwmeester
Department of Physics
University of California, Santa Barbara
Entanglement between
Light and Matter
Abstract:
Several experiments at the
interface of quantum optics and
solid-state physics will be
presented. The first experiment
addresses the generation of
multi-photon entangled state
containing up to 100 photons in a
quantum entangled state. The
second set of experiments
addresses self-assembled
quantum dots in photonic crystals
and micropillars and the search for
cavity quantum electrodynamics in
such systems. The third
experiment extends the analogy
between quantum dots and
artificial atoms to the level of
artificial molecules: the optical
properties of two vertically
stacked quantum dots are studied.
The fourth experiment addresses
the combination of nanocrystals
and microtubules and DNA tubes
to obtain insight in energy
transport properties of those
biological structures. The last
experiment addresses the
possibility of producing a
macroscopic quantum
superposition of a tiny mirror. All
projects are based on
interdisciplinary collaborations, in
particular with the groups of Pierre
Petroff (quantum dots), Evelyn Hu
(photonic crystals), Larry Coldren
(micropillars) and Deborah
Fygenson (microtubules and DNA)
at the University of California at
Santa Barbara.
(Host: Nöckel)
November 18
Using optical tweezers for
single-molecule
biophysics studies
Abstract:
Nancy Forde
Physics Department
Simon-Fraser University
Vancouver, Canada
The ability to exert force on single
molecules offers an experimental
means to probe mechanical
processes and to see beyond the
ensemble average. Optical
tweezers, which use a focused
laser beam to manipulate
micron-sized dielectric particles
with nanometer precision, allow us
to exert and detect forces on the
picoNewton scale. By attaching
molecules of interest to these
particles, we can determine
molecular response to applied
mechanical force. In this talk,
aimed at a general audience, I
will discuss the application of this
technique to studying the
movement of RNA polymerase
along DNA in real time. RNA
polymerase is a molecular motor
that catalyzes synthesis of an RNA
polymer chain, converting
chemical energy into mechanical
force causing directed movement
along the DNA template. By
studying this transcription reaction
by single molecules of RNA
polymerase, and applying a
mechanical force to assist or
oppose translocation along DNA,
we have been able to follow, and
in some cases alter, the reaction
kinetics in real time.
(Host: Linke)
December 2
Electrical noise in the
nervous system: or
"What can biophysics
learn from condensed
matter physics?"
Abstract:
Nick Giordano
Department of Physics
Purdue University
Detailed models of neurons,
axons, and dendrites are widely
used to study action potential
generation and propagation in the
nervous system. These models are
based largely on measured
properties, such as the density of
ion channels and their behavior,
so rather detailed comparisons
with observed nervous system
properties seem possible.
However, in only a few cases do
the models attempt to account for
realistic sources of noise and
fluctuations. Moreover, the
assumed noise sources are at odds
with direct studies of the electrical
noise observed in real neurons. In
this talk I review the electrical
properties of the nervous system,
and describe the "standard model"
of noise in nurons. I then show
how this model, in its current
form, is incapable of describing
the noise found in real neurons. A
new theory to explain this noise,
based on recent work in
condensed matter physics, is
proposed, and compared with
some new experimental
measurements. If our theory is
correct, it suggests a way to use
measurements of neuronal noise
to probe ion channel properties in
new and quite detailed ways.
(Host: Nöckel)
Last modified: Tue Nov 9 21:40:36 PST 2004
Jens Nöckel <[email protected]>