PHY 676 Solid State Seminar

Schedule for Spring, 1999

All talks are in Room B-131, except when otherwise noted. Regular seminar time is Friday 1:00PM. Here are links to the schedule for Spring, 1997 Fall, 1997, Spring, 1998 and Fall, 1998. Members of the Condensed Matter faculty are welcome to add speakers to the list.

• Thursday, January 21, 11:30 AM
  A. Shnirman
  (University of Illinois)
  "Resonant states and order-parameter suppression near point-like impurities in d-wave superconductors"
  
• Friday January 22, 1:00 PM
  Dr. Piet Brouwer
  (Harvard University)
  "The random magnetic flux problem in a quantum wire"
  
• Friday January 29, 1:00 PM
  A. Bachtold
  (U. Basel)
  "AB oscillations in carbon nanotubes"
  Aharonov-Bohm oscillations and other quantum transport phenomena in multiwalled carbon nanotubes. Electrical transport has been studied through single multi-walled carbon nanotubes attached to nanofabricated metal contacts. The observation of universal conductance fluctuations and one dimensional weak-localization shows that transport is governed by quantum diffusion. Since a nanotube may be viewed as a conducting cylinder, a very interesting situation arises for the longitudinal magnetic field alignment in which magnetic flux penetrates the cylinder: the resistance is observed to oscillate periodically with the field. In addition to the Aharonov-Bohm oscillation with period h/2e, a new type of Aharonov-Bohm oscillations has been discovered.
  
• Friday February 5, 1:00 PM
  D. Parshin
  (St. Petersburg)
  "Multifractal wavefunctions in disordered systems"
  
• Friday February 12, 1:00 PM
  Yuri Khavin
  (Rutgers)
  "Electron transport in quasi one dimensional conductors in the vicinity of the Thouless crossover and in the strong localization regime "
  We report on the experimental study of electron transport in sub-micron-wide ''wires'' fabricated from Si delta-doped GaAs. These quasi-one-dimensional (Q1D) conductors demonstrate the crossover from weak to strong localization with decreasing the temperature. On both sides of the crossover, the resistance has been measured as a function of temperature, magnetic field, and applied voltage for different values of the electron concentration, which was varied by applying the gate voltage. We find that on the weak localization side of the crossover the temperature dependence of the phase coherence time does not saturate and the quasiparticle states remain well defined down to the crossover temperature. This fact, as well as observation of the crossover in Q1D conductors, argues against the theory of intrinsic decoherence by the zero-point fluctuations of electrons. On the insulating side of the crossover the activation temperature dependence of the resistance has been observed with the activation energy close to the mean energy spacing of electron states within the localization domain. The study of non-linearity of the current-voltage characteristics provides information on the distance between the critical hops which govern the resistance of Q1D conductors in the strong localization regime. Below the crossover temperature, we observe the exponentially strong negative magnetoresistance due to the universal magnetic-field dependence of the localization length in Q1D conductors. This magnetoresistance is orbital (it vanishes in the parallel magnetic field) and provides a direct method of measurement of the localization length.
  
• Friday February 19, 1:00 PM
  Frank Göhmann
  (ITP, Stony Brook)
  "Correlations in the 1D interacting electron gas"
  
• Monday, February 22, 4:00 PM (Special seminar, Joint with Atomic Physics Group)
  Leonid Levitov
  (MIT)
  "Exchange collisions in a Bose gas"
  We will discuss novel many-body effects in Boltzmann and Bose gases. At low temperature the momentum relaxation is provided by momentum exchange collisions, rather than by elastic collisons. A collective excitation mode forms, which in a Boltzmann gas is manifest in a collision shift and dramatic narrowing of spectral lines. In the BEC state, due to the effect analogous to that of the second sound, spectral lines split into dublets.We present a theory of the line doubling, and calculate the oscillator strengths and linewidth.
  
• Friday February 26, 1:00 PM
  Ehoud Pazy
  (The Hebrew University, Jerusalem)
  "One dimensional phonon coupled electron tunneling"
  The problem of a tunneling electron coupled to phonons is of fundamental interest as well as potentially being of great technological importance. In this talk I will consider the case of an electron with a given energy E tunneling through a rectangular barrier where it is coupled to acoustic phonons. A realistic electron phonon interaction (deformation potential, piezoelectric) is consid- ered. Calculation of the transition probability in the one dimensional case will be presented using the Feynman path-integral method. The main effect of the phonons is a static lowering of the potential barrier. It will be shown considering the dynam- ical corrections that the problem of the complex non-linear coupling of a tunneling electron to phonons is equivalent to that of an electron tunneling through a slow uctuating spatially uniform barrier. Results for the average energy change of the tunneling electron due to phonon emission will also be presented.
  
• Friday March 5, 1:00 PM
  Prof. C.M. Marcus
  (Stanford)
  "Dephasing in quantum dots"
  
• Friday March 12, 1:00 PM
  CM group members
  (SUNY, Stony Brook)
  "Practice talks for the March Meeting of the APS"
  
  
• Friday March 19, 1:00 PM
  Dr. Yuri Pashkin
  (Japan Science and Technology Corporation and NEC Fundamental Research Laboratories, Tsukuba, Japan)
  "Recent experiments on single-electron tunneling at NEC"
  
  
• Monday April 5, 11:30 am
  Jens Nöckel
  (University of Dresden)
  "Illuminating Chaos: Microlasers as Photonic Billiards"
  
  
• Wednesday April 7, 2:15 PM
  Jan von Delft
  (University of Karlsruhe)
  "Superconductivity in Ultrasmall Grains"
  
  
• Friday April 9, 1:00 PM
  Dr. Alexey Bezryadin
  (Harvard)
  "Novel Coulomb devices based upon graphite nanoparticles"
  
  
• Friday April 16, 1:00 PM
  Hernán Makse
  (Schlumberger-Doll Research)
  "Pattern Formation in Granular Matter: from Sandpiles to Sand Dunes"
  
  
• Wednesday April 21, 1:00 PM
  Jinwu Ye
  (Johns Hopkins University)
  "Berry Phase Theory in Colossal Magneto-Resistance (CMR) Manganites"
  
  
  Friday April 23, 1:00 PM
  Daniel Agterberg
  (Florida State U and National Magnet Lab)
  "Spin Triplet Superconductivity in Sr₂RuO₄"
  
  
• Monday April 26, 1:00 PM
  Maya Paczuski
  (University of Houston)
  "Self-Organizing Networks"
  
  
• Tuesday May 4, 1:00 PM
  Felix von Oppen
  (University of Cologne)
  "Dipolar Quasiparticles for the Half-Filled Landau Level"