PHY 676 Solid State Seminar

Schedule for Spring, 1998

• Friday January 30, 1:00PM
Gwyn Williams
Brookhaven National Laboratory, NSLS)
"Synchrotron Based Infrared Investigations of Solids and Surfaces"

• Friday, February 6, 1:00 PM
  Sergey Kravchenko
  (City College of City University of New York)
  "Insulator-conductor transition in strongly interacting 2D electron system"
  
• Friday February 13, 1:00 PM
  Jeffrey Kash
  (IBM Research Division)
  "Hot Luminescence from CMOS Circuits: A Picosecond Probe of Internal Timing"
  Picosecond pulses of hot electron luminescence have been observed from individual submicron FET's in CMOS circuits. The emission is coincident with logic state switching. We explain the physics behind this switching-induced emission, and demonstrate that it is intrinsic to all CMOS circuits. A system has been constructed that simultaneously images and time resolves this emission, allowing parallel measurements on hundreds or thousands of logic gates. With this technique, which we have named PICA (Picosecond Imaging Circuit Analysis), the internal operation of integrated circuits from a simple oscillator to a full microprocessor has been measured. Videos of the emission will be shown which allow direct visualization of the complete operat ion of a circuit. Circuit delays as short as 30 psec have been directly measured.
  
• Friday February 20, 1:00 PM
  J. K. Jain
  (S.U.N.Y. Stony Brook)
  "Quantitative confirmations of the composite fermion theory"
• Friday February 27, 1:00 PM
  V. Muthukumar
  (BNL)
  "Acoustogyric effects in Antiferromagnets"
  
• Friday March 6, 1:00 PM
  Dr. V. J. Emery
  (Brookhaven National Lab)
  "A Perspective on the Theory of High-Tc Superconductivity"
  
• Friday March 13, 1:00 PM
  Xiaohui Wang
  (Department of Theoretical Physics, Lund University)
  "Coulomb blockade with strong tunneling"
• Friday March 27, 1:00 PM
  David Goldhaber-Gordon
  (MIT)
  "The Kondo Effect in a Single Electron Transistor"
  The confined droplet of electrons interacting with the leads of a single electron transistor (SET) is closely analogous to an impurity atom interacting with the delocalized electrons in a metal. A new generation of SETs exhibits the Kondo effect, the formation of a spin-singlet state between an unpaired electron in the droplet and a cloud of electrons at the Fermi level in the leads. By tuning the parameters of the SET, the physics of the Kondo problem may now be studied over a range of conditions not easily accesible to previous calculations or experiments, providing new insights into this fundamentally important problem.
  
• Friday April 3, 1:00 PM
  Prof. Sankar Das Sarma
  (University of Maryland)
  "Understanding the c-axis optical properties of high temperature superconductors using simple ideas"
  
• Wednesday April 8, 1:00 PM (SPECIAL SEMINAR, NOTE THE DATE!)
  Michael E. Gershenson
  (Rutgers University)
  "Electrons in Quasi-1D Conductors: from high-temperature diffusion to low-temperature hopping"
  I will discuss the observation of the Thouless crossover from weak to strong localization in quasi-one-dimensional (Q1D) conductors with decreasing the temperature, and the study of the hopping conductivity in these conductors on the 'insulating' side of the crossover. The samples are sub-micron-wide 'wires' fabricated from Si delta-doped GaAs. The observed crossover to the insulating state is driven by both localization and interaction effects; the main features of the crossover are in agreement with the Thouless' scenario. On the insulating side of the crossover, the activation temperature dependence of the resistance has been observed. The activation energy of the electron hopping is close to the mean energy spacing of electron states within a localization domain. The study of the non-linearity of the I-V characteristic in the strong localization (SL) regime provides information on the distance between the critical hops which govern the resistance: at low temperatures, this distance exceeds the localization length by more than an order of magnitude. We observe the exponentially strong negative magnetoresistance in the SL regime. This orbital magnetoresistance is due to the universal magnetic-field dependence of the localization length in Q1D conductors: the localization length doubles in strong fields! This universality provides a direct method of measurement of the localization length in Q1D conductors. Finally, I will discuss how to probe the density of states in Q1D conductors without doing tunnel measurements.
  
• Friday April 10, 1:00 PM
  Prof. G. Murthy
  (Boston University)
  "Hamiltonian Field Theory of the Fractional Quantum Hall Effect"
  
• Friday April 17, 1:00 PM
  Dr. Elaine DiMasi
  (BNL)
  "X-Ray Scattering Studies of Liquid Metal and Alloy Surfaces"
  
• Friday, April 24, 1:00 PM
  David Cox
  (Brookhaven National Laboratory)
  "Charge, orbital and magnetic ordering, and phase separation in CMR manganate systems'"
  
• Friday May 1, 1:00 PM
  Karin Dahmen
  (Harvard University)
  "Disorder Induced Critical Scaling: from Magnets to Earthquakes"
  
  
• Monday May 4, 11:00 AM (NOTE THE DATE AND TIME!)
  James Hone
  (UC Berkeley)
  "Thermolectric power and thermal conductivity of single walled carbon nanotubes"
  
  
• Friday May 8, 1:00 PM
  Serguei Brazovskii
  (Landau Institute, BNL and Los Alamos NL)
  "X-Ray Observation of Friedel Oscillations and of the Strong CDW Pinning in Alloys of Quasi 1D conductors."
  Impurities in metals are known to originate Friedel Oscillations (FOs) of the electronic density and/or to affect generic ones like the Charge Density Wave (CDW). Being replicated by the lattice, the oscillations may be detected by X- Rays especially in Quasi 1D metals with their divergent susceptibility (Kohn anomaly) near the Fermi surface diameter 2k_F. We report on the first such observation and on the corresponding theoretical contribution. The +/-2k_F satellite reflections in the W- and V doped Blue Bronzes K_0.3MoO₃ show two pronounced features: an asymmetry of intensities (IA) between +/-2k_F and an asymmetry of each of the +/-2k_F profiles which are distorted unusually in the same direction along the chains. The IA signifies on the scattering by the impurity induced lattice distortions. The profile asymmetry comes from phase shifts of electronic wave functions by the impurities. The temperature dependence from the RT till 20K through the Peierls transition at 183K, and a comparison between isovalent W and charged V impurities ensures us in observation of a crossover from the FO to the strong pinning of the CDW.

  In collaboration at the Laboratoire de Physique des Solide -Orsay and the European Synchrotron Radiation Facility -Grenoble, France.