Quasiparticles in High Temperature Superconductors

Chair, P. A. Lee (MIT)

Session Description:
The transport properties of high temperatures superconductors are a long-standing mystery. Recent experimental work has deepened the mystery, as photoemission measurements of the quasiparticle lifetimes become more detailed and precise, and differences between quasiparticle and transport times seem to become more pronounced. This session will focus on the comparison between transport and quasi- particle lifetimes, and the implications of these for the fundamental physics of the materials.

J. Cerne (SUNY Buffalo): "Magneto-Optics of High Temperature Superconductors"

J. C. Campuzano (U.I.C. and Argonne): "Quasiparticle Scattering in High Temperature Superconductors: the ARPES View"

Broken Symmetries in the Quantized Hall Regime

Chair: A. H.MacDonald (University of Indiana)

Session Description:
Strong correlations in the quantum Hall regime give rise to a wide variety of effects, including some associated with broken symmetry ground states. Spontaneous interlayer phase coherence in double-layer systems gives rise to collective inter-layer tunneling, and in single-layer systems unidirectional charge-density waves give rise to macroscopically anisotropic transport coefficients. In addition, rich generalizations of conventional ferromagnetism can be realized when three or more Landau levels are nearly degenerate.

J.P. Eisenstein (CalTech)

W. Pan (Columbia/FSU) "Anisotropy of Electronic Transport in the Quantum Hall Regime"

Sean Barrett (Yale) "Optically pumped NMR in the quantized hall regime"

Low Carrier Density Ferromagnets

Chair, Z. Fisk, (Florida StateUniversity)

Session Description:
This session will focus on nontraditional ferromagnets and the methods used to measure and understand them.

Mike Zhitomirsky (Institute for Theoretical Physics, Switerland) "Excitonic Ferromagnetism"

S. L. Cooper (University of Illinois at Urbana-Champaigne)

Interacting Mesoscopics

Chair: C. Marcus, (Harvard)

Session Description:
This session will emphasize how strong electron-electron interactions in confined systems such as quantum dots and quantum wires greatly enriches the character of quantum interference. One often considers mesoscopic fluctuations to be mildly influence by interactions, leading for instance to small corrections to conductivity and decoherence. As interactions become sizeable, quantum transport can enter entirely new regimes of behavior, such as the Coulomb blockade. The manifestations of mesoscopic intereference in this regime is a new and very interesting subject.

D. Ralph (Cornell)

I. Aleiner (SUNY-Stony Brook)

M. Devoret (Saclay)

Mott and Spin Liquid Effects in 3He Films

Chair, W. P. Halperin (Northwestern)

Session Description:
This symposium features investigations of 2D properties in solid and fluid 3He monolayer films on very smooth substrates (e.g. graphite preplated in various ways). These systems provide a wonderful opportunity to study a range of fundamental problems including frustration, quantum size effects,localization and correlation effects in 2D fermion systems.

Evolution of strong finite temperature deviations from Fermi Liquid behavior have been observed in magnetic susceptibility and heat capacity of the 2D fluid monolayer of 3He. The quasiparticle effective mass ratio increases from unity at low densities and appears to diverge as the critical density for solidification is aproached, consistent with Mott localization.

A quantum spin liquid state appears in the second-layer solid 3He adsorbed on graphite. This system is known to be an ideal 2D nuclear magnet with spin 1/2. Because of competition between the multiple spin exchanges and a triangular lattice structure the ground state of the low density 2D antiferromagnetic solid can be highly frsutrated without any long ranged order. The competition can be tuned by changing density and the underlying lattice symmetry since the multiple spin exchange frequencies strongly depend on the geometrical configuration of the surrounding atoms.

The 2D solid He and other 2D cryocrystals can be studied in real space with scanning tunnelling microscopy (STM). Tunnelling measurements have been performed to significantly below 100mK but it still remains a significant challenge to observe quantum mechanical tunnelling of a single atom with the STM technique.

J. Saunders (Royal Holloway College, London) "Correlations in two dimensional fluid 3He"

A. Fukuyama (Tokyo)

Disorder and Impurity Effects in Correlated Electron Systems

Chair, H. Alloul (Orsay)

Session Description:
Impurities and point defects are charge and/or spin perturbations which can be introduced in a controlled manner in materials. The non-local response of the host can be used to probe its spin and charge properties and the relationshiop between the two. The great potential importance of such an approach for elucidating the physics of correlated electron systems will be discussed.

J.Bobroff (Orsay) "Effect of Spinless Impurities in high-Tc cuprates from NMR Studies"

V. Kiryukhin (Rutgers) "Phase Diagram of Doped Spin-Peierls Systems"

S. Sachdev (Yale) "Impurity Spin Dynamics in 2D Antiferromagnets"

Novel Superconductors

Chair, F. Steglich, (MPI Dresden)

Session Description:
Studies of unconventional superconductivity in non-cuprate materials in recent years have broadened our knowledge of superconductivity with rich and new perspectives. Sr2RuO4, which is isostructural to the 214 cuprates, becomes superconducting below Tc = 1.5 K. Convincing evidence of an unconventional, i.e. p-wave, symmetry of the gap function will be presented. UPd2Al3 is a heavy-fermion (HF) compound in which local-moment AF order (TN = 14.5 K) coexists with HF superconductivity below Tc = 2 K. Analysis of inelastic neutron scattering data within the "dual model" of two localized and one itinerant 5f electrons as well as comparison with tunneling data leads to the suggestion that UPd2Al3 is a strong-coupling magnetic-exciton mediated superconductor, with a polar shape of its gap function.

N.K. Sato (Nagoya) "Magnetic Exciton Mediated Superconductivity in UPd_2Al_3"

A. Mackenzie (Birmingham) "Magnetism and Superconductivity in Ruthenates"

Nonequilibrium Physics of Correlated Systems

Chair, Joseph Orenstein (University of California, Berkeley)

Session Description:
The rapid development of 'fast optics' techniques and high power lasers has created new opportunites in the experimental studies of correlated electron systems., involving both measurements on heretofore inaccessible timescales and an previously unattainable regimes. This session will present some of the new experiments which begin to demonstrate the power of the new techniques and to raise new questions.

J. Dodge (Lawrence Berkeley Laboratory)

M. Woerner (Berlin) " Femtosecond Spectroscopy of High Temperature Superconductors"

J. Kikkawa (University of Pennsylvania) "All Optical Nuclear Magnetic Resonance"

Late Breaking Developments

Chair, M. Aronson (U. Michigan)

Session Description:
This, the concluding session, will focus on new directions in the physics of correlated electron systems.

E. W. Plummer (Oak Ridge) "Defect mediated phase transitions in 2-D: From charge density waves to defect density waves"

Bertram Batlogg (Lucent Technologies)