September 13, 2004
Controlling Quantum Properties of Carbon Nanotubes
Dr. Nadya Mason
University of Illinois at UrbanaChampaign
Detailed studies of carbon nanotube physics and
devices require independent control of nanotube parameters. It is
particularly important to control electron confinement (quantum dot)
and constriction (point contact) effects for applications such as
quantum computation. In this talk, I will show how we achieve independent
control of nanotube parameters via multiple electrostatic gates. Local
gates can be used to fabricate and measure nanotubebased quantum dots
and quantum point contacts. I will discuss how this control of a nanotubebased
double quantum dot allowed us to manipulate and study singleelectron
charging effects as well as charge interactions within the nanotube.
I will also discuss the appearance of quantized conductance steps when
local gates are used to create pointcontactlike constrictions in nanotubes.

September 20,
2004
(Fe,Co)Si, A SiliconBased Magnetic Semiconductor
Prof. John DiTusa
Louisiana State University
Doping the Kondo insulator FeSi with Co at the
Fe site leads to a ferromagnetic metal that is fully spin polarized
below the Curie temperature. I will present transport, magnetic, and
optical data that reveal that the transport in this material is highly
senstive to external magnetic fields. All of these quantities reveal significant
effects of quantum interference effects of the diffusively conducting carriers.
As such the behavior is not like more standard magnetic semiconductors or
half metallic materials.

September 27, 2004
Heat Conductivity in Spin
Chains and Ladders
Prof. Natan Andrei
Rutgers University
We outline a general approach to the computation
of transport properties of interacting systems at low temperetures
and frequencies. We show that if the fixed point and the irrelevant
operators around it are known, then by studying the structure of the
softly violated conserved currents chracterizing the fixed point one
may set up an effective calculation in terms of a memory matrix formalism.
We apply this approach to the computation of thermal conductivity of
spin chains and ladders embedded in a matter matrix and interacting with
its phonons. The results are found to be in very good agreement
with experiment.

October 5, 2004
How Good is the DMRG Approach to Quantum Hall
Systems?
Prof. Barry Friedman
Sam Houston State University
A density matrix renormalization group (DMRG) approach,
has recently been developed by Shibata and Yoshioka to treat quantum Hall
systems. This computational method has the ability to treat larger system
sizes then other accurate ³unbiased² numerical methods (i.e. the
³gold standard² in the field, direct diagonalization). This
opens up the possibility of accurate numerical treatment of compressible
systems, for example, stripes, Wigner crystals and bubble states. In the
first part of the talk, a review of the dmrg method suitable for a general
audience will given and an introduction to the quantum Hall effect (in
the context of semiconductor physics, no atomic gases!) will be provided.
The second part of the talk will present our preliminary numerical
results for the DMRG applied to high Landau levels.

October
25, 2004
Thermal Transport in Metallic Nanostructures
Prof. Venkat Chandrasekhar
Northwestern University
As the size scale of electronic devices continues
to decrease, the dissipation of heat generated in device operation becomes
a critical problem, and understanding the mechanism of heat transport
in nanostructures becomes of increasing importance. This aspect of the
physics of nanostructures is only beginning to be explored. In this talk,
I will outline the techniques we have developed to perform thermal measurements
on nanostructures, and the results of our experiments on thermal transport
in devices incorporating normalmetals and superconductors, where a number
of new and interesting effects are observed.

November 29, 2004
Condensed matter physics with cold atom systems:
vortex pinning, superconductivity and ferromagnetism
Dr. Rembert Duine
University of Texas at Austin
The experimental realization of BoseEinstein condensation
in a dilute atomic gas has inspired a lot of theoretical and experimental
work on these systems. One of the many interesting properties of these systems
is their suitably to engineer hamiltonians, wellknown from condensed matter
physics, in a very controllable way. Perhaps the bestknown example along
these lines is the use of an optical lattice to engineer the socalled BoseHubbard
hamiltonian, and study its Mottinsulator to superfluid phase transition,
as has been achieved recently. In this talk, I'll discuss other examples
of ideas from condensed matter physics applied to the field of atomic gases.
First, I'll show that a BoseEinstein condensate in a corotating optical
lattice provides an excellent system to study the pinning of vortices and
structural transitions between different types of vortex lattices. After
this, I will consider fermions and briefly discuss the possibility of experimentally
realizing and detecting the BardeenCooperSchrieffer state, known from
the theory of superconductivity. The latter state occurs for attractive
interatomic interactions, and I'll also briefly discuss the possibility of
realizing a ferromagnetic state for the case of repulsive interatomic interactions.

January 24, 2005
Conductance in One Dimension: Nanotubes and Molecules
Prof. Michael Fuhrer
University of Maryland
Recent advances have allowed the exploration of
true onedimensional electron transport in two new systems: carbon nanotubes
and conjugated organic molecules. In each case electrons are conducted
through the extended orbital network of carbon. I will discuss recent
experiments in my lab to determine the fundamental conduction properties
of semiconducting carbon nanotubes, and recent results from a collaborative
effort to synthesize, measure, and model transport through individual organometallic
molecules. Growth of very long (up to 1 millimeter), very clean semiconducting
carbon nanotubes has allowed determination of the charge carrier mobility
in this material. The mobility may exceed 105 cm2/Vs at room temperature,
higher than any other known semiconductor. Schottkybarrier electrodes
allow simultaneous injection of electrons and holes at high bias, with recombination
in the nanotube. A simple model allows determination of the saturation
velocity of carriers in the nanotube of 2 x 107 cm/s, twice that in silicon.
We have studied the conduction through a ferrocenebased organometallic
molecule, and, in excellent agreement with theoretical results, observe
a Lorentzian resonance in the biasdependent conduction with a peak differential
conductance of up to 70% of Go, the theoretical maximum. The results
are in sharp contrast to those of our group and other groups on conjugated
allorganic oligomers, where a high conductance resonance is also expected,
but not observed experimentally. We suggest some solutions to this
dilemma.

February 24, 2005
Photoexcited zeroresistance states in the high
mobility 2DES
Prof. Ramesh Mani
Harvard University
We summarize experimental observations relating
to novel photoexcited vanishing resistance states in the ultra high mobility
2DES at low temperatures, in a large filling factor limit. GaAs/AlGaAs Under
microwave photoexcitation, GaAs/AlGaAs 2DES specimens exhibit vanishing
diagonal resistance, without Hall resistance quantization, about B = 4/5
Bf and B = 4/9 Bf, where Bf = 2π f m*/e, m*
is the electron mass, e is electron charge, and f is the EMwave frequency,
as the resistanceminima follow B = [4/(4j+1)] Bf with j=1,2,3…
In this report, we illustrate the basic characteristics and highlight supplementary
features, in light of recent theory for this remarkable effect.

March 28, 2005
STMinduced light emission from metal surfaces
and quantum well systems
Prof. Peter Johansson
Chalmers University
This talk will give a review of STMinduced light
emission from a variety of systems: metal surfaces, semiconductors, molecules
etc. I will then focus on discussing light emission from metallic quantum
well states, an effect displaying an interesting interplay between enhanced
spontaneous light emission due to plasmon resonances and the electronic structure
of the quantum well system, an Na overlayer on a Cu(111) surface.

April 04, 2005
TwoChannel Kondo Behavior in a ThreeLevel System
with partially broken SU(3) Symmetry
Prof. Hans Kroha
Universität Bonn
Although the intriguing nonFermi liquid signatures
of the twochannel Kondo (2CK) effect, have been observed in several nanoscopic
transport experiments, A clear microscopic model for its realization is still
lacking even after a decade of research.
After a brief review of the experimental situation and the theoretical difficulties
for the stabilization of the 2CK fixed point, a physical realization of the
2CK effect will be proposed in this talk, where a dynamical defect in a metal
has a partially broken SU(3) symmetry with a unique ground state and twofold
degenerate excited states. The defect can be comprised of an interstitial
atom moving in a modulated Mexican hat potential, which is formed by the
lattice. A perturbative renormalization group analysis shows that the coupling
to the conduction electrons renormalizes the excited defect levels below
the noninteracting ground state, thus stabilizing the 2CK fixed point. For
a wide range of parameters the level crossing occurs in the weak coupling
region. The model may explain, on the same footing, the 2CK zerobias anomaly
and the conductance spikes observed in ultrasmall metallic point contacts.
