All talks are in Room
B-131, except when otherwise noted. Regular seminar time is Friday
1:30PM. Follow the links to see the schedule in past semesters.
Yakov S. Greenberg
(
Novosibirsk State Technical University
):
Rabi spectroscopy of the interferometer-type
superconducting qubits
The density matrix formalism is applied to analyze the
interaction of the interferometer-type superconducting
qubit with a high-quality tank circuit with frequency
which is well below the gap frequency of a qubit. By
making use of a dressed state approach we describe
the qubits' spectroscopy in the situation when the qubit
is also irradiated by a microwave field tuned to the gap
frequency.
Host: Averin
February 8, Friday, 1:30PM
Jukka Pekola
(
Low Temperature Laboratory, Helsinki University of Technology, Finland
):
TBA
A hybrid tunnel junction between normal metal and superconductor
(NIS-junction) constitutes a building block for a number of devices.
Electronic refrigeration and thermometry in NIS-devices has been studied
for over one decade by now. Adding Coulomb effects allows one to control
both the heat flow and the electric current by a gate. Recently we have
proposed and tested experimentally a few new types of Coulomb blockaded
NIS-devices: I will present in my talk a radio-frequency single-electron
refrigerator, a Brownian refrigerator, a heat transistor, and finally
a hybrid single-electron turnstile.
Host: Averin
March 28, Friday, 1:30PM
Sergei M. Stishov
(
Institute for High Pressure Physics,
Russian Academy of Sciences,
Troitsk, Moscow):
Experimental study of magnetic phase transition in the itinerant helimagnet
MnSi at ambient and high pressure
Host: Allen
April 4, Friday, 1:30PM
Alexander Orlov
(
Stony Brook University, Materials Science
):
Surfaces, Interfaces, and Nanoparticles: environmental and
optical properties
Combining solar light with photocatalysts can destroy a variety of dangerous pollutants in air and water. It is potentially a
very powerful method to clean up the contaminated environment. However, there are still many challenges concerning the
efficiency and reliability of this approach. This project has focused on fundamental and applied aspects of visible-light
absorbing materials based on N-doped and B-doped TiO2. It has also explored the issues related to the UV light activity of
nanoparticulate gold modified TiO2. The advantage of visible light active materials as compared to UV light active materials
is much more efficient energy utilization, as the solar spectrum contains only a small UV component. In this project we have
developed various photocatalytic materials, more active than the conventional materials under both UV and visible light. Based
on theoretical calculations and model system studies we have also explored the issues of reproducibility and activity of such
materials. It appears that the overall picture of the visible light activity of these materials is very complex with most of
the published work oversimplifying the phenomena.
Host: Allen
May 2, Friday, 1:30PM
Jon Rameau
(
Brookhaven National Laboratory and Stony Brook University
):
Particle-Hole Asymmetry in the Pseudogap State of an Underdoped Cuprate.
For over twenty years the quest to understand the phase diagram of the copper oxide high temperature superconductors -- the cuprates -- has been a driving force in the development of powerful condensed matter spectroscopic techniques. Angle resolved photoemission spectroscopy (ARPES) in particular has seen an order of magnitude increase in energy and momentum resolution in that time. The modern ARPES technique, which directly measures the occupied single electron density of states of solids as a function of binding energy and crystal momentum, is now capable of resolving the fine details of electronic structure in many interesting one and two dimensional systems. In spite of these advances the cuprates have resisted a good physical understanding of their superconducting and anomalous normal state properties. In my talk I will discuss the application of some new experimental and analytical approaches to high resolution ARPES on the cuprates. These advances have allowed us to use ARPES to extract quantitative information about low-lying excited states of the cuprates in both the normal pseudogap and superconducting phases. Most importantly, the new information acquired by these techniques has revealed for the first time a relatively complete picture of the anomalous “normal” state from which high temperature superconductivity arises and provides a large set of new facts that any theory of high temperature superconductivity must be able to explain.
Host: Allen
May 9, Friday, 1:30PM
Matt Dawber
(
Stony Brook University
):
Improper ferroelectricity in perovskite oxide artificial superlattices.
A large body of work has shown that in paraelectric/ferroelectric heterostructures with thick constituent layers electrostatics is the dominant interaction between layers. From a practical sense this provides a useful route for the tailoring of materials to particular applications, however, the real excitement concerning artificially layered fine period multilayers lies in the potential for phenomena that are driven by the interfaces and present markedly different behaviors from the parent compounds. Here we discuss an example of this kind of behavior; interfacially driven improper ferroelectricity in lead titanate/strontium titanate superlattices. A combination of experimental measurements and first principles calculations are used to reveal the manner in which oxygen rotations at the interfaces in the structure couple in such a way as to drive a macroscopic polarization with properties that differ substantially from those associated with conventional ferroelectricity. These observations suggest an approach, based on interface engineering, to produce artificial materials with unique properties.
Host: Allen
May 16, Friday, 1:30PM
Ribhu Kaul
(
Harvard University
):
Destruction of Néel order in square lattice anti-ferromagnets
It has been long believed in the study of the cuprates that a thorough understanding of the possible insulating paramagnetic
phases that are proximate to the Néel ordered parent materials may hold the key to the mysterious properties that appear on
the introduction of charge carriers. The parent materials are well described by S=1/2 square lattice anti-ferromagnetic
models. Hence the destruction of Néel order in such spin Hamiltonians, which is a subject of great theoretical interest in
itself, might also shed light on one of the most exciting experimental puzzles of our time -- high-temperature superconductivity.
In this seminar, I will report numerical results on the first model S=1/2 square-lattice quantum anti-ferromagnet in which
Néel order can be destroyed and which is nevertheless amenable to unbiased sign-problem free quantum-Monte Carlo simulations.
Our numerical study which is carried out on lattices that contain in excess of 10,000 spins indicate that the paramagnetic
state that emerges on the destruction of Néel order in this model has valence-bond solid order (VBS). Close to the transition
there is evidence for quantum criticality and I will show how the observed scaling behavior may be understood by a comparison
with large-N computations on a particular continuum field theory that is expected to describe the Néel-VBS transition.
Host: Durst