CONDENSED MATTER SEMINARS
Thursdays
at
4:00 pm
in B&H 190
SPRING
2008
JANUARY
Thursday, January 31, 2008 at 4 pm B&H 190
Prof. Rumiana Dimova
Max
Planck Institute of Colloids and Interfaces, Potsdam, Germany
"Giant vesicles: a handy tool for mimicking
the cell membrane"
Abstract: Vesicles are closed lipid
bilayer compartments with an internal water core. Giant vesicles, in
contrast to conventional ones (~ 100nm), have the advantage that they
can be observed using optical microscopy. These giants, being only a
few tens of microns in size, are quite a handy tool for studying the
mechanical properties of lipid bilayers, because the physical
characteristics of the membrane can be obtained from working with
individual vesicles. A large variety of techniques have
been developed for assessing the elastic properties (bending modulus,
stretching elasticity, spontaneous curvature) and the hydrodynamic
features (shear surface viscosity) of the lipid bilayer. A few of them
will be presented in this talk. Giant vesicles have been also used for
direct observation and measuring the properties of lipid membranes when
undergoing phase transitions. A dramatic increase of the membrane
surface viscosity as well as the bending stiffness of the membrane was
detected for membranes crossing the fluid-to-gel phase transition. The
interaction of electric fields with lipid membranes and cells has been
extensively studied in the last decades. The phenomena of
electroporation and electrofusion are of particular interest because of
their widespread use in cell biology and biotechnology for gene
transfer and cancer treatment. However, direct optical microscopy
observation of effects caused by electric DC pulses on membranes is
difficult because of the short duration of the pulse. Recently this
difficulty has been overcome in our lab. Using a digital camera with
high temporal resolution, we were able to access the dynamics of
electro-deformation, –poration and –fusion of vesicles on a
sub-millisecond time scale. Results from these observations will be
presented.
Host: T. Powers
FEBRUARY
Thursday, February 7, 2008 at 4 pm B&H
190
Abstract:
Host:
Thursday, February 14, 2008 at 4 pm B&H
190
Prof. Christoph
Schmidt
Drittes Physikalisches
Institut, University of Göttingen,
Germany
"Rheology of Biological Networks
Probed by Laser Traps"
Host: J. Tang
“ ”
Host:
Thursday, February 28, 2008 at
4 pm B&H
190
Abstract:
Host:
MARCH
Thursday, March 6, 2008 at 4 pm B&H
190
Prof. Matthew P. A. Fisher,
University of California Santa Barbara
“Critical Quantum Fluids with d-wave Pair
Correlations”
Abstract: The existence of 2d Mott insulators which exhibit no symmetry breaking yet gapless excitations is suggested both by experiment and theory. Such putative “critical spin liquids” are the bosonic analog of the non-Fermi liquid phases which are arguably required in order to account for the behavior observed in the cuprates at optimal doping and in the pseudo-gap regime. Regrettably the only gapless quantum fluid states that are well understood are the Bose superfluid and the Fermi liquid. In this talk I will describe a novel quantum fluid phase of 2d bosons on the square lattice which possesses relative d-wave two-body correlations - a d-wave Bose liquid. The electronic analog, a d-wave metal, will be briefly discussed.
Thursday, March 13, 2008 at 4 pm B&H 190
APS March Meeting
Thursday, March 20, 2008
at 4 pm B&H
190
Abstract:
Host:
Thursday, March 27,
2008 at 4 pm B&H
190
APRIL
Thursday, April 3, 2008 at 4 pm B&H
190
Prof. Robin Cote
University of Connecticut
“Ultracold molecules: forming and using them”
Abstract: During the last few years, the interest in producing and manipulating ultracold molecules has led to great achievements ranging from the realization of molecular condensates to Cooper pairs formation. We will give an overview of techniques to produce ultracold molecules, paying special attention to the role of Feshbach resonances. We will then illustrate how polar molecules could be used in quantum information processing.
Thursday, April 10, 2008 at 4 pm B&H
190
Dr. Florian Schuetz,
Brown University
“Phase diagram of coupled two-leg Cu-O
ladders, a renormalization group perspective”
Abstract: Two-leg Hubbard ladders are a simple toy model to
study non-trivial electronic ordering in interacting many-electron
systems. Due to the availability of controlled analytical and numerical
methods in one dimension, their phase diagram has been extensively
studied. Experimental realizations are of a quasi one-dimensional
nature with weak two-dimensional inter-ladder hopping and interaction
terms. In particular, the Ca doped spin-ladder compound Sr14Cu24O41
has a complex phase diagram including charge-density-wave order as well
as unconventional superconductivity under high doping and high
pressure. Using a many-patch functional renormalization group scheme,
we study a model of coupled Cu2O5
ladders. We investigate instabilities towards charge, spin, and pairing
order as a function of hole doping, inter-ladder hopping, and
interaction strength.
Thursday, April 17, 2008
at 4 pm B&H
190
Prof. Carlos A. R. Sa
de Melo
Georgia
Institute of Technology and Joint Quantum Institute University of
Maryland/NIST
“The Evolution from
BCS to Bose-Einstein Condensation: Superfluidity in Metals, Neutrons
Stars, Nuclei, and Ultra-Cold Atoms”
Abstract:
Superfluidity is a very interesting phenomenon that has been found
in metals, neutron stars, nuclei and more recently in ultra-cold atoms.
For a given metal, neutron star, or nuclei there is essentially “zero”
tunability of the particle density or interaction strength, and thus
superfluid properties can not be controlled at the turn of a knob.
However, in ultra-cold Fermi atoms the interaction strength and the
particle density can be tuned to change qualitatively and
quantitatively superfluid properties. This tunability allows for the
study of the evolution from BCS (weak coupling) superfluidity of large
Cooper pairs to Bose-Einstein condensation (strong coupling)
superfluidity of tightly bound molecules. I will discuss the BCS
to BEC evolution in s-wave and p-wave angular momentum channels, and
will conclude that this evolution is just a crossover phenomenon for
s-wave, while a quantum phase transition takes place for the p-wave
case.
Host: B. Marston
Thursday, April 24, 2008 at 4
pm B&H
190, special
general HE talk, in memory of Prof. Kyungsik Kang
Prof. Matt Strassler
Rutgers
University
“ ”
Abstract:
Host: C. Tan
MAY
Thursday, May 1, 2008 at 4 pm B&H
190
Prof. Christophe Clanet
“ ”
Abstract:
Host: T. Powers
Thursday, May 8, 2008 at 1 pm B&H 190
Dr. Michael
Stewart,
Brown University
“Realization of Bosonic Insulators Near the
Superconductor-Insulator Transition”
Abstract:
Abstract: Ultra-thin amorphous films can display a startlingly
large range of electrical conductivity as their thickness or an applied
magnetic field is varied. In the T=0 limit, the conductivity
either crashes to zero or diverges to infinity. Universal models of
these quantum superconductor-insulator transitions (SIT) rest upon the
assumption that Cooper pairs occupy the insulating as well as the
superconducting state. Experimentally, no clear evidence for this
assumption has been offered. Investigations of a new film system with a
regular nanohoneycomb (NHC) array of holes demonstrate definitively,
through charge 2e magnetoresistance oscillations, the presence of
Cooper pairs in the NHC insulating phase. We discuss this observation
and others in NHC films as well as their implications for other systems.
Thursday, May 15, 2008
at 4 pm B&H
190
Abstract:
Host:
Thursday, May 22, 2008 at 4 pm
B&H
190
Abstract:
Host:
Thursday, May 29, 2008
at 4 pm B&H
190
Abstract:
Host:
Thursday, September 6, 2007 at 4 pm B&H
190
Abstract:
Host:
Thursday, September 13, 2007 at 4 pm B&H 190
Thursday, September 20, 2007 at 4 pm B&H
190
Abstract:
Host:
Thursday, September 27, 2007 at 4 pm B&H
190
Abstract:
Host:
OCTOBER
Thursday, October 4, 2007 at 4 pm B&H
190
Abstract:
Host:
Thursday, October 11, 2007 at 4 pm B&H
190
Abstract:
Host:
Prof. Petia Vlahovska
Dartmouth College
“Shape
Transitions of Vesicles in Hydrodynamic and Electric Fields ”
Host: V. Mitrovic
Friday, October 19, 2007 at 2 pm B&H 190 - Special Seminar
Prof. Ady Stern
Weizmann Institute of Science
“Proposed
Experiments to Observe Non-Abelian Anyons in the Quantum Hall Effect”
Abstract:
Host: D. Feldman
Thursday, October 25, 2007 at 4 pm B&H
190
Dr. Michel Godin
MIT
“Microdevices
for Biomolecular and Single Cell Detection”
Abstract:
Host: D. Stein
NOVEMBER
Thursday, November 1, 2007 at 4 pm B&H
190
Prof. Mayank Mehta
Brown University
“Neurophysics of Learning: How oscillations, Resonance and Symmetry
Influence the Brain Mechanisms of Learning”
Host: T. Powers
Thursday, November 8, 2007 at 4 pm B&H
190
CM & Molecular and Nanosciences
Institute Seminar
Prof. Vladimir
Goldman
Stony Brook
“Interferometry
of Electrons and
Laughlin Quasiparticles”
Two kinds of interferometer devices have been realized. In the primary-filling interferometer, the entire device has filling 1/3, and the e/3 edge channel quasiparticles encircle identical e/3 island quasiparticles. Here the flux period is h/e, same as for electrons, but the back-gate charge period is e/3. In the second kind of interferometer, a lower density edge channel at filling 1/3 forms around a higher density island at filling 2/5, so that e/3 edge quasiparticles encircle e/5 island quasiparticles. Here we observe superperiodic oscillations with 5h/e flux and 2e charge periods, both corresponding to excitation of ten island quasiparticles. These periods can be understood as imposed by the anyonic braiding statistics of Laughlin quasiparticles.
Host: D. Feldman
Thursday, November 15, 2007 at 4 pm B&H
190
Prof. Philip Kim,
Columbia University
“Electric
Transport in Graphitic Carbon Materials”
Thursday, November 22, 2007 at 4
pm B&H
190
Thanksgiving Holiday
Tuesday, November 27, 2007 at 11 am B&H 751 - Special Seminar
Prof. Yuval Geffen,
Weizmann Institute of Science
“Weak
Measurements and Weak Values: a New View of Quantum Mechanics
Applied to Solid State Systems”
Abstract:
Host:
DECEMBER
Wed., December 5, 2007
at 2 pm B&H 190 - Special Seminar
Prof. Dean Astumian,
University of Maine
“Adiabativ
Operation of a Molecular Machine”
Thursday, December 6, 2007 at 4 pm B&H 190
Abstract:
Host:
Thursday, December 13, 2007 at 4 pm B&H
190
Abstract:
Host:
Prof. Martin Greven,
Stanford University
“Recent
neutron scattering results for the high-temperature superconductors Nd2-xCexCuO4+d
and HgBa2CuO4+d”
In a separate effort, we have succeeded in growing sizable single crystals of HgBa2CuO4+d, the single-layer hole-doped compound with the highest superconducting transition temperature. Our inelastic neutron scattering results reveal that the magnetic resonance occurs at an unexpectedly high energy [3]. Finally, we discuss very recent polarized neutron diffraction data that clearly reveal the existence of “hidden” magnetic order in the pseudogap phase of HgBa2CuO4+d [4].
[1] E.M. Motoyama et al., Nature 455, 186 (2007).
[2] G. Yu et al., unpublished.
[3] X. Zhao et al., Adv. Materials 18, 3243 (2006); G. Yu et al.,
unpublished.
[4] Y. Li et al., unpublished.
Host: V. Mitrovic & B. Marston
SUMMER
2007
Thursday, June 14, 2007 at 4 pm B&H 190
Iowa State University and Ames Lab.
“Organisation of Signaling Phospholipids in the Plasma Membrane by Polybasic Protein Clusters”
Abstract:
Host: D. Stein
Thursday, June 21, 2007 at 4 pm B&H
190
Abstract:
Host:
Thursday, June 28, 2007 at 4 pm B&H 190
Abstract:
Host:
JULY
Friday, July 20,
2007 at 2:30 pm B&H 330
Institute of Physics, Academia Sinica, Taipei
"Nanoscale molecular traps and stretching tunnels"
Abstract:
In this presentation, we will focus on two nanofluidic devices: (1) molecular traps
for biomolecular focusing and (2) nanochannels for DNA stretching. The molecular
traps are constructed in dielectric substrates based on electrodeless, or insulator-
based, dielectrophoresis, employing the same physical principle as optical trapping.
An array of nanoscale dielectric constrictions is defined using a combination of photo-
and electron-beam lithography on nanofluidic passages. Upon the application of an
external ac electric field, the field will be focused at the constrictions and high
field gradient can be generated to trap molecules dynamically in aqueous solutions.
Small DNA or protein molecules may be focused in an array of these nanoscale molecular
traps down to 50 nm in size. Nanofluidic channels are also constructed using reverse
nanoimprinting and a newly developed room-temperature composite sealing process. We
have demonstrated the stretching of bacteriaphage DNA in these nano-confined
environments with channel diameters comparable to the persistence length of DNA that
opens up new opportunities for the study of DNA statics and dynamics, DNA-protein
interactions and direct mapping of protein binding sites along DNA. Ultralow aspect
ratio 2D-confined nanochannels with channel height less than 10 nm are also
constructed for the study of fluidic and biomolecular behaviors approaching the 2D
limit.
Host: S. Ling
SPRING 2007
JANUARY
Thursday, January 25, 2007 at 4 pm B&H 190
Abstract:
Host:
FEBRUARY
Thursday, February 1, 2007 at 4 pm B&H 190
Prof. Eugene Demler
“Measuring correlation functions in
interacting
systems of cold atoms”
Probabilistic nature of quantum mechanics is evident most directly in
the
existence of quantum noise. In strongly interacting many-body systems
we expect
quantum noise to reveal nonlocal correlations of the underlying states.
In this
talk I will discuss how measuremnts of noise in experiments with cold
atoms can
be used to investigate the unusual character of quantum many-body
states.
Host: V.
Mitrovic
Thursday, February 8, 2007 at 4 pm B&H 190
Abstract:
Host:
Thursday, February 15, 2007 at 4 pm B&H 190
Prof. Pengcheng Dai
The University of Tennessee/Oak Ridge National
Laborator
“Nature of Quantum Spin Correlations through
magnetic-field-induced superconducting-normal
phase transition in electron-doped
high-Tc
superconductor Pr0.88LaCe0.12CuO4”
Abstract:
We briefly review results of recent
neutron
scattering experiments designed to probe the evolution of
antiferromagnetic
(AF) order and spin dynamics in the electron-doped Pr0.88LaCe0.12CuO4
as the
system is tuned from its as-grown non-superconducting AF state into an
optimally doped superconductor (Tc = 24 K) without static AF order
[1-4]. As
grown, electron-doped materials are semiconducting with static
long-range AF
order, annealing the sample in low oxygen environment removes the
static AF
order and induces superconductivity. On the other hand, application of
a magnetic
field can also induce superconductivity-normal phase transition.
In this
seminar, I will summarize how one can use annealing and magnetic field
as
tuning parameters to study the superconducting-normal phase transition.
Our
results demonstrate an intimate relationship between antiferromagnetism
and
superconductivity in electron-doped superconductors, and suggest that
AF spin
fluctuations may mediate electron pairing for superconductivity.
1 Stephen D. Wilson, Pengcheng
Dai,
Shiliang Li, Songxue Chi, H. J. Kang, and J. W. Lynn, Nature (London)
442, 59
(2006).
2 Stephen D. Wilson, Shiliang Li, Hyungje Woo, Pengcheng Dai, H. A.
Mook, C. D.
Frost, S. Komiya, and Y. Ando, Phys. Rev. Lett. 96, 157001 (2006).
3. Stephen D. Wilson, Shiliang Li, Pengcheng Dai, Wei Bao, J. H. Chung,
H. J.
Kang, S.-H. Lee, S. Komiya, and Y. Ando, Phys. Rev. B 74, 144514 (2006).
4. H. J. Kang, Pengcheng Dai, B. J. Campbell, P. J. Chupas, S.
Rosenkranz, P.
L. Lee, S.L. Li, S. Komiya, and Y. Ando, Nature Materials (in press)
cond-mat/0701345.
Host: V. Mitrovic
Thursday, February 22, 2007 at 4 pm B&H 190
Prof. Richard Stratt
“The fast onset of slow dynamics”
Abstract:
Materials such as
supercooled liquids become increasingly different from ordinary liquids
as they
approach the glass transition. Diffusion constants begin to drop
by
orders of magnitude, for example. One place to look for an
explanation is
the exceptionally rough potential energy landscape that these systems
all have
in common. But what is it about the landscapes that accounts for
the
dynamics? We suggest that the key feature is purely geometric:
the
rapidly growing lengths of the shortest (geodesic) paths that traverse
the
landscape. We test this idea by finding these paths in a
computer-simulation of a glass-forming liquid - an interesting
numerical
problem in its own right, but one we can tackle using ideas borrowed
from the
robotics literature.
Host: D.
Feldman
MARCH
Thursday, March
1,
2007 at 4 pm B&H 190
Dr. Ulrich Keyser
Universitaet of Leipzig
“Solid-State Nanopores: Nanobubbles,
Single-Molecule Sensing, and the Force on DNA”
Abstract:
Amongst the variety of roles for
nanopores in
biology, an important one is enabling polymer transport, for example in
gene
transfer between bacteria and transport of RNA through the nuclear
membrane.
Recently, this has inspired the use of protein and solid-state
nanopores as
single-molecule sensors for the detection and structural analysis of
DNA and
RNA by voltage-driven translocation. We discuss in detail our
experimental
approach to localize nanopores [1] and to understand the origin, namely
nanobubbles, of instable ionic currents hindering DNA-detection in
nanopores [2].
The magnitude of the force during the voltage-driven translocation of
DNA is of
fundamental importance in understanding and exploiting this
translocation
mechanism, yet so far has remained unknown. Here, we demonstrate the
first
measurements of the force on a single DNA molecule in a solid-state
nanopore by
combining optical tweezers with ionic current detection [3]. The
opposing force
exerted by the optical tweezers can be used to slow down and even
arrest the
translocation of the DNA molecules. This new techniques allows full
control
over single DNA strands in a single nanopore. We obtain a value of
0.24±0.02
pN/mV for the force on a single DNA molecule [1], independent of salt
concentration from 0.02M to 1M KCl. We compare this with data from free
DNA translocation
[4] and discuss the implications for the screening of DNA by
counterions in
solution.
[1] U. F. Keyser et al. Nano Letters 5, 2253 (2005)
[2] R. M. M. Smeets, U. F. Keyser et al. Phys. Rev. Lett. 87, 088101
(2006)
[3] U. F. Keyser et al. Nature Physics 2, 473 (2006)
[4] R. M. M. Smeets, U. F. Keyser et al .Nano Letters 6, 89 (2006)
Host: D.
Stein
Thursday, March 8, 2007 at 4 pm B&H 190
March Meeting
Thursday, March 15, 2007 at 4 pm B&H 190
Dr. Walter Reisner
The Physics of DNA in Nanochannels
Abstract:
Understanding the behavior of dsDNA in confined geometries at the
single-molecule level is crucial to the development of bionanofluidic
technology for chip-based analysis systems.
When the device dimension falls below characteristic molecular
scales
(e.g. the radius of gyration, persistence length), qualitatively new
physical
regimes are reached in which statistical properties of the
macromolecule
deviate from their values in bulk and become functions of the degree of
confinement. When confined in effectively
1D dimensional channel structures (both height and depth in the
nanoregime),
DNA is observed to stretch out in such a way that the extension along
the
nanochannel is linearly proportional to the contour length. This proportionality establishes a one-to-one
correspondence between position along the DNA and position with the
genetic
code that can be used to correlate the action of enzymes or fluorescent
probes
to specific genetic sequences. This talk
will present scaling arguments and experimental data on the basic
physics of
DNA stretching in silica nanochannels with dimensions ranging from
400nm to
35nm, including the effect of varying device dimensions and solution
ionic
strength. Ionic strength is observed to
have a surprisingly strong effect on the extension, which we ascribe to
an
electrostatically enhanced DNA effective width.
We will also discuss designs and preliminary data on a new
nanoslit
'nanogroove' architecture that might be used to locally change the
chemical
environment of the nanoconfined molecules and concentrate molecules in
the
nanochannels.
Host: S.
Ling
Thursday, March 22, 2007 at 4 pm B&H 190
Abstract:
Host:
Thursday, March 29, 2007 at 4 pm B&H 190
Spring Break
APRIL
Thursday, April
5,
2007 at 4 pm B&H 190
Prof. Aniket Battchyra
Cental University of Florida
“DNA translocation through protein and
synthetic nano pores”
Abstract: DNA
translocation through narrow protein channels is recognized as an
important process in biology. Recently it has attracted lot of
attention in the biophysical community following several experiments on
DNA translocation through protein nano-pores, and more recently,
through synthetic silicon nano-pores. A fundamental understanding is
needed for various biological processes, e.g., entry and exit of a DNA
in and out of a cell, efficient separation methods for macromolecules,
and, possibly fast DNA sequencing. In this talk I will be presenting
results for the DNA translocation using a coarse-grained model for an
idealized DNA as well as the pore. I will consider several scenarios
for the DNA translocation.
First, I will show scaling of translocation time of
a homopolymer as it escapes from the trans side to thecis} side of an
idealized thin membrane[1]. Then I will consider DNA dynamics subject
to a driving force inside the pore.
Next, I will consider heteropolymer threading
through a nano-pore[2]. Specifically we will consider both highly
ordered and completely random sequences of the chain and relate
specific sequences to the distribution of the translocation time and
the residence time inside the pore. These studies also will include
effects due to different environment on either side of the pore,
specific DNA-pore interactions located at selective sites, etc.. I will discuss relevance of
these simulation results to recent experiments and theoretical models.
1. A. Milchev, K. Binder, and Aniket Bhattacharya, J. Chem. Phys. 121, 6042 (2004).
2. Kaifu Luo, Tapio Ala-Nissila, See-Chen Ying, and Aniket Bhattacharya (to appear in J. Chem. Phys.)
Host: See-Chen. Ying
Thursday, April 12, 2007 at 4 pm B&H 190
"50 Years of the BCS Theory of Superconductivity" - Conference
Thursday, April 19, 2007 at 4 pm B&H 190
Prof. Robert Austin
Princeton University
“The City of Cells”
Abstract:
Host: S.
Ling
Thursday, April 26, 2007 at 4 pm B&H 190
Prof. Vesna Mitrovic
“Inhomogeneous Superconductivity”
Abstract: Nuclear magnetic resonance (NMR)
measurements were used to investigate a possible inhomogeneous
superconducting state (Fulde-Ferrell-Larkin-Ovchinnikov - FFLO) of
CeCoIn5 stabilized at the low temperature in the vicinity of Hc$_2$.
The FFLO state emerges as a result of interplay between the gain of
magnetic energy, due to the polarization of quasiparticle spin via the
Zeeman effect, and the loss of superconducting condensation energy in a
magnetic field when the pairs with opposite spins are depaired. In this
state, the superconducting order parameter varies periodically in real
space and Cooper pairs acquire finite momentum. The nature of the FFLO
state as revealed by NMR will be discussed.
Host:
C.
Elbaum
MAY
Thursday, May 3,
2007
at 4 pm B&H 190
Abstract:
Host:
Thursday, May 10, 2007 at 4 pm B&H 190
Abstract:
Host:
Thursday, May 17, 2007 at 4 pm B&H 190
Abstract:
Host:
Thursday, May 24, 2007 at 4 pm B&H 190
Abstract:
Host
FALL
2006
OCTOBER
Thursday, October 5, 2006 at 4 pm B&H 190
Abstract:
Host:
Thursday, October 12, 2006 at 4 pm B&H 190
Abstract:
Host:
Thursday, October 19, 2006 at 4 pm B&H 190 -
CM &
HET Seminar
Prof. Aad Pruisken
University of Amsterdam
“Exact Haldane mapping for all S and super
universality in spin chains”
Abstract:
Host: M. Kosterlitz
Wednesday, October 25, 2006 at 4 pm B&H 190
Prof. Nikolai Prokofiev
University of Massachusetts
“Superfluid disorder in quantum solids ”
Abstract:
I will briefly review old ideas on how can superfluidity occur in a crystalline solid, briefly mention a theorem that any supersolid in continuous space must be in the incommensurate state and have gapless vacancies and/or interstitials. In He-4 vacanices and interstitials are gapped, and thus ideal crystals are insulating. I will present path-integral Monte Carlo data to prove that. To explain recent experiments on the non-classical moment of inertia of He-4 solids one has to consider various types of disorder. I will show examples of superfluid defects in lattice and helium systems, and discuss which of them are likely to be present in experimental samples. Finally, I will discuss the "ultimate" superfluid disordered state - a helium superglass which we observed to be remarkably stable at low temperatures and elevated pressures.
Host: D. Feldman
NOVEMBER
Thursday, November 2, 2006 at 4 pm B&H 190
Dr. Michael Hermele
MIT
“Spin liquids near the Mott transition”
Abstract:
Host: B. Marston
Thursday, November 9, 2006 at 4 pm B&H 190
Dr. Igor Beloborodov
Argonne National Laboratory
“Artificial Nanosolids”
Abstract:
Artificial nanosolids, arrays of nanoscale grains interacting with each other through electron tunneling, offer rich new horizons of novel macroscopic behavior emerging from nanoscale structure and dynamics. Fundamental microscopic phenomena such as Coulomb correlation, disorder and coherence produce dramatically new and programmable bulk behavior when mediated by nanoscale granular structure. Each building block of these new materials can be viewed as a tiny cluster of atoms of metallic, semiconducting or superconducting elements. These clusters are not as small as molecules but not as large as macroscopic objects. I will review our progress made in the last several years in understanding the properties of artificial nanosolids. In particular, I will discuss the following topics:
1)
Introduction to physics of artificial nanosolids
2) Novel transport regimes
3) The phase diagram of artificial nanosolids
4) Future opportunities
Reference
I. Beloborodov et al., Reviews of Modern Physics, 79(2) (2007);
cond-mat/0603522
Host: D.
Feldman
Thursday, November 16, 2006 at 4 pm B&H 190
Prof. Ranjan Mukhopadhyay
Clark University
“Curvature-mediated microphase separation and lipid
localization in cell membranes”
Abstract:
Recent research has demonstrated a surprising degree of protein organization and seggregation on bacterial membranes. Could lipid domains play a role in protein organization? Indeed the phospholipid cardiolipin has been shown to localize to the poles of rod-shaped bacteria. In this talk, I will introduce a minimal model for cell wall mediated microphase separation that produces domains with some characteristic size and demonstrate that this provides a robust mechanism for lipid localization and sequestering of proteins. We will discuss the relevance of our model to recent experimental findings and to systems such as lipid rafts.
Host: J. Tang
Thursday, November 23, 2006 at 4 pm B&H 190
Thanksgiving Holiday
Thursday, November 30, 2006 at 4 pm B&H 190
Abstract:
Host:
DECEMBER
Thursday, December 7, 2006 at 4 pm B&H 190
Prof. Peter
Nightingale
University of Rhode Island
“Excited states: a quantum
Monte
Carlo approach”
Abstract:
I shall discuss the basics of the computation of low-lying energy
eigenstates states of van der Waals clusters. A powerful test of this
approach
exploits the identity (for S states) of the spectra of an N particle
system in
N−1 and N +1 spatial dimensions. In addition to a brief sketch of the
origin of this interdimensional degeneracy, and its
implications, I
shall present a review of instabilities that haunt these Monte Carlo
calculations, and discuss in some detail a solution of one particular
problem
that arises in this context, namely the construction of a robust
guiding
function that efficiently samples several different excited states
simultaneously.
Host: B.
Pelkovits
FEBRUARY
Thursday, February 2, 2006 at 4 pm B&H 190
Prof. Julia Meyer
“Spontaneous Spin
Polarization
in Quantum Wires”
Abstract: A number of recent experiments report spin
polarization in
quantum wires in the absence of magnetic fields. These observations are
in
apparent contradiction with the Lieb-Mattis theorem, which forbids
spontaneous
spin polarization in one dimension. We show that sufficiently strong
interactions between electrons induce deviations from the strictly
one-dimensional geometry and indeed give rise to a ferromagnetic ground
state
in a certain range of electron densities. At higher densities, more
complicated
spin interactions lead to a possibly novel ground state.
Host: D.
Feldman
Thursday, February 9, 2006 at 4 pm B&H
190 Moved to March
30, 2006
Prof. Dobrin P.
Bossev
Indiana University
"Bending Elasticity of Lipid Bilayers Studied by
Neutron Spin Echo Spectroscopy"
Abstract:
Host: S.
Ling, I. Dimitrov
& N.
Daniilidis
Abstract:
Host:
Thursday, February 23, 2006
Dr. Pavel Kraikivski
Max-Planck Institute of Colloids and Interfaces,
Potsdam,
Germany
"Polymer manipulation and motility on substrates"
Abstract:
Two
subjects related to the non-equilibrium dynamics of polymers or
biological filaments adsorbed to two-dimensional substrates will be
discussed. The first part is dedicated to thermally activated dynamics
of polymers on structured substrates in the presence or absence of a
driving force. The structured substrate is represented by double-well
or periodic potentials. Both homogeneous and point driving forces are
considered. Point-like driving forces can be realized in single
molecule manipulation by atomic force microscopy tips. Uniform driving
forces can be generated by hydrodynamic flow or by electric fields for
charged polymers.
The second part
is dedicated to collective filament motion in motility
assays for motor proteins, where filaments glide over a motor-coated
substrate. The model for the simulation of the filament dynamics
contains interactive deformable filaments that move under the influence
of forces from molecular motors and thermal noise. Motor tails are
attached to the substrate and modeled as flexible polymers (entropic
springs), motor heads perform a directed walk with a given
force-velocity relation. I willconsider the collective filament
dynamics and pattern formation as a function of the motor and filament
density, the force-velocity characteristics, the detachment rate of
motor proteins and the filament interaction. In particular, the
formation and statistics of filament patterns such as nematic ordering
due to motor activity or clusters due to blocking effects are
investigated.
MARCH
Dr. Antti-Pekkar Hynninen
Princeton University, Princeton
"Binary Crystal Structures -
from Charged Spheres to Hard Spheres"
Abstract: Micrometer-sized particles (ëcolloidsí) suspended in a solvent form important model systems for atoms and molecules. They display the same phase behaviour (gas-fluid-solid), but are easier to investigate and manipulate. I will present simulation results on two binary systems: (i) oppositely charged colloids and (ii) mixtures of large and small hard spheres. In the case of oppositely charged colloids, we find colloidal analogs of many atomic structures, doped fullerene C60 structures, and new structures. In the case of large and small hard spheres, our findings pave the way for the self-assembly of the colloidal diamond structure.
Host: See-Chen Ying
Prof. Rama Bansil
Boston University, Boston
"Gelation: How it Keeps the Stomach From Digesting
Itself"
Abstract: In this talk, I will
describe the unusual polymeric properties of mucin, a high molecular
weight glycoprotein found in mucus, which is responsible for protecting
the stomach from being digested by the gastric juices that it secretes.
Using dynamic light scattering we were able to show that purified pig
gastric mucin solutions form a gel under acidic pH. Tapping mode atomic
force microscopy of mucin solutions and gels as a function of pH
provide direct visual evidence of aggregation. AFM studies on human
mucus will also be presented. A model of gelation based on the
interplay of hydrophobic and electrostatic interactions will be
discussed. I will also describe how the acid is transported
across the mucus layer by the viscous fingering instability mechanism.
Host: Jay Tang
Thursday,
Abstract:
Host:
Thursday, March 23, 2006 at 4 pm B&H 190
Dr. Hakho Lee
Center for Molecular Imaging Research, Massachusetts
General
Hospital / Harvard Medical School
“Hybrid IC / Microfluidic
Chips
for the Manipulation of Biological Cells”
Abstract: A hybrid IC / Microfluidic chip that can manipulate
individual biological cells in a fluid with microscopic resolution has
been demonstrated.
The chip starts with a custom-designed silicon integrated circuit (IC)
produced
in a semiconductor foundry using standard processing techniques. A microfluidic chamber is then
fabricated on top of the IC to provide a
biocompatible environment.
The motion of biological cells in the chamber is controlled using a
two-dimensional array of micro-scale electromagnets in the IC that
generate
spatially patterned magnetic fields. A
local peak in the magnetic field amplitude traps a magnetic bead and an
attached cell; by moving the peak's location, the bead-bound cell can
be moved
to any position on the chip surface. By generating multiple peaks, many
cells
can be moved independently along separate paths, allowing many
different
manipulations of individual cells. The
hybrid IC / Microfluidic chip can be used, for example, to sort cells
or to
assemble tissue on micrometer length scales. To prove the concept, an
IC /
Microfluidic chip was fabricated, based on a custom-designed IC that
contained
a two-dimensional microcoil array with integrated current sources and
control
circuits. The chip was tested by
trapping and moving biological cells tagged with magnetic beads inside
the
microfluidic chamber over the array. By combining the power of silicon
technology
with the biocompatibility of microfluidics, IC / Microfluidic chips
will make
new types of investigations possible in biological and biomedical
studies.
Host:
S. R.
Park
Prof. Dobrin P. Bossev
Indiana University
"Bending Elasticity of Lipid Bilayers Studied by
Neutron Spin Echo Spectroscopy"
Abstract: The physical boundaries of the living cell
and its organelles are defined by bio-membranes made of phospholipids
bilayers. In this presentation we focus on a particular mechanical
property of the membranes, bending elasticity, which is directly
related to the thermal undulations. The importance of the undulations
is that they predetermine the contact time and the interaction of the
cell or the organelle with the surrounding elements and substrates. In
reality there are more than 200 types of lipids that constitute the
lipid membranes as well as additional components such as cholesterol
and membrane proteins. We have chosen model membranes, made of single
type of lipid, to investigate the bending elasticity in the presence of
cholesterol, addition of electrolyte, and as a function of temperature
using Neutron Spin Echo (NSE) technique. NSE is the most direct method
to monitor the thermal undulations of the lipid bilayers in solution
because it is a unique scattering technique that covers the time scale
of 0.01 – 100 ns, characteristic of these motions. We have used the
Zilman-Granek approach to interpret the decay of the intermediate
scattering function and to evaluate the bending modulus of elasticity,
k, of the lipid bilayers. The results are compared to those obtained by
other methods and possible explanations of these effects are also
discussed in the scope of the bilayer structure.
Host: S.
Ling, I. Dimitrov
& N.
Daniilidis
APRIL
Dr. Buddhapriya Chakrabarti
Harvard University, Boston
"Nanopore translocation and Shear
denaturation of DNA"
Abstract: Single molecule biophysics research has
recieved a lot of attention in recent years. In this talk I focus on
two important areas i) translocation of biopolymers through nanopores
and ii) unzipping of double stranded DNA. In particular I describe our
recent theoretical work on DNA hairpin retraction from a nanopore
assisted by an electric field and shear unzipping of ds-DNA.
Host: S. Ling
Thursday, April 13, 2006
Prof. Z. Schlesinger
University of California, Santa
Cruz
"Using infrared spectroscopy to
study strongly correlated and complex materials"
Abstract: Infrared and optical spectroscopy cover a range from about 0.001 eV to 5 eV encompassing most of the interaction scales important to condensed matter physics phenomena. These techniques have been widely used to study the origins of unusual electronic phenomena including high-temperature superconductivity, bad metal behavior and heavy-Fermion physics. A quite different example, based in unconventional phonon dynamics, is the phenomenon of large, sustained negative thermal expansion (NTE) in Zr(WO4)2. Potential applications abound, however there are materials related issues, and our understanding of the mechanism of NTE and its remarkable stability in Zr(WO4)2 is limited. Recent results suggest that underconstraint, a concept central to the understanding of frustration in magnetic systems, plays an essential role. This talk will introduce infrared spectroscopy, and explore its ability to help elucidate the relationship between nanoscale structural underconstraint, highly unusual phonon dynamics, and the macroscopic phenomenon of negative thermal expansion.
Host: V. Mitrovic
Thursday, April 20, 2006 at 4 pm B&H 750
Dr. Cedomir
Petrovic
Brookhaven National Laboratory
"New Intermetallic Model Systems"
Abstract: In the recent
years, several types of new intermetallic materials have renewed
interest in intermetallics as model systems. In this talk, I will
review synthesis methods, basic physical properties and some aspects of
anisotropy of MgB2 and new superconducting series of heavy fermion
superconductors CeMIn5 (M=Rh,Ir,Co). In the case of MgB2
I will address the basic mechanism of superconducting state and I will
present temperature and field dependence of its fundamental properties.
Work on CeMIn5 will be presented in historical context,
progressing from the discovery of 115 superconducting family, and
ending with recent results on the gap anisotropy in CeCoIn5.
I will also present study of magnetic, transport and structural
properties of small gap semiconductor FeSb2 and I will
discuss possible Kondo Insulator – like characteristics. This will be
followed by some topics from current research, research philosophy and
opportunities for graduate students.
Host: V.
Mitrovic
Thursday, April 27, 2006 at 4 pm B&H 190
Prof. Elbio R. Dagotto
"Recent Computational Studies of
Strongly Correlated Electronic Systems in Bulk and Nanoscopic Forms"
Abstract: In this seminar a summary of recent results
obtained using computational techniques in the context of strongly
correlated electronic systems will be presented. This includes (1)
results for manganites, the materials with the colossal
magnetoresistance, (2) phenomenological studies of high temperature
supercondutors, and (3) transport studies of nanoscopic systems where
strong correlation cannot be neglected.
Host: B.
Marston
Friday, April 28, 2006 at 2 pm B&H 190 - Special Seminar
Dr. Manuel Cardona
Max Planck Institute,
Stuttgart
"Einstein's Legacy as the
Father of Condensed Matter Physics"
Abstract:
Host: C. Elbaum
MAY
Prof. Maxim Vavilov
Yale University
"Electron Energy Spectrum
in an Andreev Billiard"
Abstract: I will discuss the energy spectrum of a small metal grain connected to a superconductor, called an Andreev billiard. Near the Fermi level, the electron density of states in a grain is suppressed due to the Andreev reflection of electrons at the boundary between metal and superconductor. I will analyze how the strength of a disordered potential in a metal grain affects the electron density of states. Particularly, I will show that the limit of strong disorder corresponds to the random matrix description of Andreev billiards. In the opposite limit of weak disorder, the density of states approaches the semiclassical solution. However, I will demonstrate that even in clean systems the semiclassical solution cannot be reached as a result of the interplay of classically chaotic dynamics and quantum diffraction of electron wave packets.
Host: D. Feldman
Friday, May 5, 2006 at 2 pm B&H 190 - Special Seminar
Prof. Arun Paramekanti
University of Toronto
"Superfluids on the Brink
of Supersolidity"
Abstract:
Host: B. Marson
Prof. Alexei Kitaev
California Institute
of Technology
"Protected Qubits Using
Josephson Junctions"
Abstract: Several schemes of
topological protections
have been proposed, in which qubits are realized as degenerate ground
states of quantum many-body systems so that all likely perturbations
are exponentially suppressed. I will describe a particular approach
based on a ``quantum transformer'', a superconducting current mirror
operated in the quantum regime. This is a four-terminal device whose
energy depends only on $\phi_1-\phi_2+\phi_3-\phi_4$, with
exponentially small ``error terms'' like $\cos(\phi_1-\phi_4)$. The
qubit is implemented by connecting
terminal 1 with 3 and 2 with 4. I will discuss a realization of
the basic element, as well as qubit measurements and unitary gates.
Host: D.
Feldman
Wednesday, June 14, 2006 at 3 pm B&H 190, Special Seminar
Prof. X.Z. Zhao
MIT and Wuhan
University
"Solid State Electrolyte
Dye-sensitized Solar Cell"
Abstract: Dye-sensitzed solar cell (DSSC) is a potential substitute for conventional and expensive silicon-based solar cell. Replacing liquid state electrolyte with solid state electrolyte in DSSC is a multidisciplinary challenge faced by researchers in physics, chemstry, and materials science and engineering. Progress in this field will be discussed.
Host: S.
Ling
AUGUST
Dr. Kwon Park
University of Maryland
of the Strong Coupling BCS
Hamiltonian and the t-J Model"
Abstract:
Host:
Sang Ryul Park
SEPTEMBER
Prof. Liviu
Movileanu
Syracuse University
“Stochastic
sensing with a protein pore"
Abstract:
We have
developed a new strategy to examine single polymer dynamics within a
protein nanopore, a simple system that is highly relevant to
several more complex biological processes such as the translocation of
nucleic acids and polypeptides through
transmembrane pores. We have used rational design and chemical
modification of the transmembrane pore of ?-hemolysin to
devise unusual nanostructures with movable tethered polymeric arms. The
ionic current through a single nanopore was
determined by single-channel electrical measurements in lipid bilayers.
The results revealed unprecedented details of polymer
behavior under confinement at the single molecule level. In addition, a
variety of stochastic sensing devices for small molecules or
macromolecular analytes were derived. We also tethered a single
oligonucleotide within the same nanopore to allow DNA duplex
formation inside the pore lumen. This nanostructure revealed details of
the DNA duplex kinetics difficult to obtain by
conventional methods, like surface plasmon resonance, which measure
ensemble properties.
Thursday,
September 22,
2005
at 4pm B&H 190
Abstract:
Friday,
September 23,
2005
at 4pm MM 115
Special Nano-Science Seminar
& Chemistry Colloquium
Prof. Younan Xia
University of Washington
"Shape-Controlled Synthesis of Nanostructured Materials"
Abstract:
Abstract:
OCTOBER
Monday, October 3,
2005
at 4pm B&H 190
Special Nano-Science Seminar
Series
Prof. Jin-Feng Jia
Beijing National
Laboratory for Condensed Matter Physics, Institute of Physics, the
Chinese Academy of Sciences
Abstract:
[2] Y. F. Zhang, J. F. Jia, T. Z. Han, et al., Phys Rev. Lett. 95 (2005) 096802
Host: Eng. Division
Thursday, October 6,
2005
Prof. Charles (Chip) Lawrence
Brown Universit
"RNA
Secondary Structure Prediction: Statistical Mechanics Approach"
Abstract:
Host: B. Pelkovits
Prof. Oleg Tchernyshyov
Johns Hopkins University
"Condensation of magnons and spinons in
magnetic field"
Abstract:
Host: V. Mitrovic
Dr. Oleg Trushin
The Russian Academy of Science
"Mechanisms of strain relief in
heteroepitaxial systems"
Abstract:
Hong Kong
"Charge and Current Structures
in the Field induced Zero Resistanc State"
Abstract:
Within the spirit of Ginsburg-Landau theory for
superconductors, we construct a semi-phenomenological transport
equation to study the spontaneously generated charge and current
structures in a system with negative-resistance instability generated
by applied (DC) magnetic and (AC) electric fields. We obtain a
non-trivial phase diagram of charge and current structures which shows
zero-resistance behavior. In particular, one of the phases can explain
the unexpected temperature-dependent resistance in the experimentally
observe Radiation-Induced Zero Resistance State in 2D electron gases.
Abstract: