-
Aviad Frydman
(University of California, San Diego)
"Magnetoresistance of Granular Ferromagnets - Observation of a Magnetic Proximity Effect?"
Abstract Can a magnetic layer induce ferromagnetism in a nearby non-magnetic layer? Can one observe a magnetic proximity effect analogous to the well-known effect in superconductivity? In my talk I will present an experiment designed to try to detect such an effect. The magnetoresistance of a film of small Ni grains covered by a non magnetic layer is measured as a function of various overlayer materials (Pd, Ti, Ag, Cu and Ge). These measurements show that the intermediate non-magnetic media couple between the magnetic grains and give rise to a large magnetic particle size. The effect is strong for paramagnets, weaker for diamagnets and does not exist when the intermediate material is an insulator. These data are interpreted as possible signs of a proximity effect in which the itinerant conduction electrons in the ferromagnet generate a magnetic moment in a non-magnetic metal.
-
Dr. Frank Hekking
(Ruhr-Universitat Bochum, Germany)
"Anomalous Thermal Transport in Quantum Wires"
Thermal transport in a one-dimensional quantum wire, connected to reservoirs is studied. Despite of the absence of electron backscattering, interactions in the wire strongly influence thermal transport. Electrons propagate with unitary transmission through the wire and electric conductance is not affected. Energy, however, is carried by bosonic excitations (plasmons) which suffer from scattering even on scales much larger than the Fermi wavelength. If the electron density varies randomly, plasmons are localized and charge-energy separation occurs. The effect of plasmon-plasmon interaction will also be discussed, using Levinson's theory of nonlocal heat transport.
-
Dr. Ned Wingreen
(NEC Research Institute, Princeton)
"Designability of Protein Structures"
The protein structures found in nature represent only a small fraction of all possible folded configurations. A simple lattice model for protein folding has helped identify a principle of 'designability' which may explain the existence of this preferred class. The highly designable structures, i.e. those which are the ground states of a large number of sequences, have other protein-like properties such as thermodynamic stability, fast folding, and geometrically regular appearances. A mapping of the hydrophobic model onto a geometrical representation explains both the origin of highly designable structures and the close relation between designability and thermodynamic stability.
-
Prof. Konstantin Likharev
(SUNYSB)
"More Mesoscopic Research News from European Laboratories"
-
Dr. Michael Reyzer
(Ohio State University)
"Effect of gapless collective excitations on kinetics of two-dimensional electron systems"
It is known that collective excitations in a clean two-dimensional electron system, the plasmons, are gapless. We show that corresponding singularity in the electron-electron ineraction leads to a nonanalytic structure of the one-particle electron density of states similar to a well-known Altshuler-Aronov singularity in an impure electron system associated with the diffusion mode. Then we study the collective excitations and their effect on the tunneling conductance in clean symmetric and clean-disordered asymmetric two-dimensional tunneling contacts. We also study interference corrections to the conductivity and the Hall conductivity of weakly disordered electron systems.
-
A. Odintsov
(Delft University of Technology)
"Transport of interacting electrons in modulated quantum wires and carbon nanotubes "
-
Dr Fei Zhou
(Princeton)
"Mesoscopic mechanism of adiabatic charge transport"
We consider adiabatic charge transport through mesoscopic metallic samples caused by a periodically changing external potential. Both the amplitude and the sign of the charge transferred through a sample per period are determined by the quantum interference.
-
Alexander N. Korotkov
(Moscow State University and SUSB)
"Continuous quantum measurement of a double-dot"
Continuous measurement of a two-level system (double-dot) by weakly coupled detector (tunnel point contact nearby) is studied. While usual treatment leads to the gradual system decoherence due to the measurement, we show that the knowledge of the measurement result can restore the pure wavefunction at any time (this can be experimentally verified). The formalism allows to write a simple Langevin equation for the random evolution of the system density matrix which is reflected and caused by the stochastic detector output. Gradual wavefunction 'collapse' and quantum Zeno effect are naturally described by the equation.
-
Myron Strongin
(BNL)
"Infrared Studies of Localization in Ultra-thin Films"
-
Jose L. Jimenez
(Beckman Institute, U. of Illinois, Urbana)
"A New Photodetector Device: The Quantum Dot Spectrometer"
A Quantum Dot Spectrometer (QDS) is a novel photodetector device that can read and distinguish the different spectral lines of an optical signal, much in the way a conventional spectrometer does, but has the size, however, of a conventional semiconductor photodiode. Thus, it has the capability to be integrated in arrays. The QDS has two functional units: a quantum dot plane with an inhomogeneus dot size distribution to perform the optical detection and a double resonant-tunneling structure to perform the spectrally sensitive electronic read-out. In this talk, we will present the idea behind the device and its possibilities, as well as its limitations. To sustain the viability of the proposed device, we will present simulations of the structure using realistic models based on the 3D Schroedinger equation.
-
Martha Greenblatt
(Dept. Chemistry, Rutgers University)
"Large Low-field Magnetoresistance in CaCu3Mn4O12, a Perovskite-like Oxide with Hetero-Magnetic-Ion Coupling"
-
Prof. Gayanath Fernando
(U. Conn. (Storrs) and BNL)
"Density Functional Theory and Beyond: Where do we go from here?"
Modern day Density Functional Theory (DFT) has been remarkably successful in a wide variety of condensed matter systems. This fact has been recognized by the Nobel committee in awarding the 1998 Nobel prize in Chemistry to one of the founders of this theory, Walter Kohn, who is sharing it with a chemist. However, there are some notable failures of DFT (and its spin polarized version), such as in dealing with the antiferromagnetism in the normal states of the high temperature superconductors. I will examine our current understanding of DFT, its successes as well as its inadequacies. Some of our attempts to go beyond the above formalism using effective action based ideas and model Hamiltonians will be briefly discussed with specific results from Fe-N systems.
-
Prof. M. Ogawa
(Kobe University)
"Applications of Non-equilibrium Green's Functions to Quantum Transport in Semiconductor Microstructures"
Many-body effects play an important role in many of the physical phenomena that govern solid-state devices. In this talk, we will show that a formalism based on nonequilibrium Green's functions provides a natural way to study the kinetic properties of a many-body quantum system. As applications of the method, we will present a model of quantum transport in GaAs/AlAs resonant tunneling diodes that includes space-charge and scattering effects, and a model of Coulomb oscillation and transport characteristics in quantum dots.
-
Prof. Bruce Harmon
(Iowa State University, Ames)
"Recent Developments in Spin Dynamics"
-
Götz Bendele
(SUNY, Stony Brook)
"Buckminsterfullerene: Charge State, Dimerization and Polymerization (PhD Defense)"
You are visitor #
since 1/29/1998.
Send comments to Phil Allen ; last updated 3/30/98.