• Thursday, August 23, 11:00AM
  Dr. Elena Cimpoiasu
  (Kent State University)
  Magnetotransport in Antiferromagnetic YBa₂Cu₃O_6.25 Single Crystals.
  Host: Likharev


• Friday, September 7, 1:30PM
  Prabhakar Pradhan
  (Northeastern University)
  Statistics of the eigen function of chaotic and disordered systems
  Host: Likharev


• Friday, September 14, 1:30PM
  Boris Laikhtman
  (Hebrew University)
  Phase diagram of quasi-2D electron-hole gas in single and double quantum wells
  Host: Likharev


• Friday, September 21, 1:30PM
  Vladimir Falko
  (University of Lancaster, UK)
  Effect of in-plane magnetic field on transport in chaotic quantum dots
  Host: Aleiner


• Friday, September 28, 1:30PM
  Sergey A. Vitkalov
  (City College of the City University of New York)
  Scaling behavior of the magnetoconductivity of dilute 2D electrons: transition to a spin ordered state
  Dilute strongly interacting systems of electrons or holes have been the focus of intense recent interest. Contrary to expectations based on theory for weakly interacting electrons and earlier experiments, the resistivity of these systems displays metallic temperature dependence in the absence of a magnetic field over some range of densities above a critical density n_c. An unusual property of these materials is their enormous response to external magnetic fields applied parallel to the plane of the electrons (holes): depending on density and temperature, the conductivity of silicon MOSFETs decreases substantialy with magnetic field and saturates to a field-independent value above a magnetic field H_s of several Tesla. In this talk, I will discuss two experimental findings:
  (1) at high electron density, measurements in magnetic fields applied at small angles relative to the electron plane in silicon MOSFETs indicate a factor of two increase of the frequency of Shubnikov-de Haas oscillations at H > H_s; this signals the onset of full spin polarization above H_s
  (2) for densities near the apparent M-I transition the in-plane magnetoconductivity of silicon MOSFETs demonstrates scaling behavior with magnetic field H of
  We suggest that the 2D dilute electron system undergoes a magnetic transition.
  Host: Aleiner


• Friday, October 5, 1:30PM
  Oleg Tchernyshyov
  (Princeton)
  The world's most frustrated magnet
  Frustrated magnets are distinguished by horrendously degenerate ground states. Nominally small perturbations---quantum or thermal fluctuations, coupling to other degrees of freedom and the like---compete to lift this degeneracy and produce a variety of phases: Neel, paramagnetic, spin liquid, spin glass, spin ice, a valence-bond solid. I will discuss recent progress in our understanding of pyrochlore antiferromagnets, fine examples of this species, with a focus on quantum "order by disorder" and a semiclassical "order by distortion" that explains many features of a peculiar spin-Peierls transition observed in several cubic spinels (cond-mat/0108505).
  Host: Aleiner


• Friday, November 2, 1:30PM
  Bulbul Chakraborty
  (Brandeis University)
  Topological jamming and the glass transition
  Host: Allen


• Friday, November 9, 1:30PM
  Dmitry Gutman
  (Weizmann)
  How to detect shot noise at high temperatures?
  We consider the possibility of measuring shot noise of at high temperatures. We demonstrate that odd order correlation functions are determined by the non-equilibrium part of the current fluctuations even in high temperature (small bias) regime. For a quasi-one-dimensional diffusive constriction we calculate the third order cumulant of the current fluctuations (S_3), deriving its full temperature dependence. We study the effect of the inelastic collisions among the electrons. It turns out that these do not affect the value of the third order current cumulant in the high temperature limit. This renders S_3 a potentially attractive object for experimental study.
  Host: Aleiner


• Friday, November 16, 1:30PM
  Stephen O'Brien
  (Columbia)
  Oxide Nanoparticles and Nanostructured Materials. Synthesis Strategy and Size Dependent Properties
  Nanotechnology provides scientists with the opportunity to contemplate new roles for materials that are, or possess modulation on the nanometer scale. We are also faced with the difficult task of producing new materials that will allow us to identify and study phenomena associated with this length scale. Following recent developments in chemical techniques for producing highly monodisperse nanoparticles of semiconductors. We have been working on ways to adopt these methods and apply them to the synthesis of highly monodisperse binary and ternary oxide systems. Among them are ferroelectric oxides, BaTiO₃ and magnetic iron oxides Fe₂O₃ (gamma phase, maghemite) and Fe₃O₄ (magnetite)
  Host: Allen


• Friday, November 30, 1:30PM
  Pierre Fazan
  (Swiss Federal Institute of Technology, Switzerland)
  SOI Devices, DRAM Memories and a New Semiconductor Memory Concept
  In this presentation we will first introduce Silicon On Insulator (SOI) MOSFETs, and the Floating Body (FB) effects associated to Partially Depleted (PD) SOI MOSFETs. We will then review the architecture, structure and concepts behind the Dynamic Random Access Memory (DRAM). The actual DRAM memory cell consists of one transistor and one capacitor (1T/1C cell). We will then present a new DRAM concept by exploiting the FB effects in PD MOSFETs. With this concept, a memory cell that consists of a single transistor and no capacitor can be realized. This cell, a capacitor-less 1T-DRAM cell, can be made two times smaller than current DRAM cells. The operation of the cell during writing and reading will be described. The data retention and device reliability will be highlighted. TCAD simulations will be used to understand the operating principles. Finally, a cell layout and integration will be proposed and the various advantages of this cell will be presented.
  Host: Likharev


• Friday, December 14, 2:00PM
  Sasha Chernyshev
  (Oak Ridge National Laboratory)
  Diluted 2D antiferromagnet: from impurity to duality
  The static and dynamic properties of quasi-two-dimensional quantum antiferromagnet diluted with spinless impurities are studied. We show that for the diluted 2D AF the spectrum is not "protected" but rather is overdamped at arbitrary concentration of impurities. Although the dynamical properties are significantly modified we show that the long-range order persists up to the percolation threshold. Thus, in low-dimensional systems with disorder connection between static and dynamic quantities is not straightforward. Our results are in quantitative agreement with the recent Monte Carlo simulations and experimental data for S=1/2, S=1, and S=5/2. We also propose other experiments which can further test the results of our theory.
  Host: Abanov

Send comments to Laszlo Mihaly; created 8/12/2001.