Physics Colloquium Schedule

FALL QUARTER 2003

Gregory S. Boebinger
National High Magnetic Field Laboratory,
Los Alamos National Laboratory

September 25, 2003

The Abnormal Normal State of the High-Tc Superconductors--or Undressing Electrons with Nearly a Million Gauss

At the National High Magnetic Field Laboratory (NHMFL) in Los Alamos, we operate an international users' program with the world's most powerful 60 tesla (600,000 gauss) pulsed electromagnets, more than a million times stronger than the Earth's magnetic field. The infrastructure includes a 1.4 Billion watt generator, the largest electrical generator in the United States, which delivers the energy equivalent of a hundred sticks of dynamite to the magnet during a magnet pulse. We employ high-tensile-strength nano-composite materials in the magnets and operate them up to the point of explosive stress failure--and occasionally beyond.

In addition to revealing what happens beyond the point of magnet failure, I will report on successful pulsed-magnetic-field experiments that suppress the superconducting state in the high-temperature superconductors, revealing the normal-state behavior in the zero temperature limit. The normal-state behavior is highly abnormal compared to conventional metals: (1) there is an unusual localization behavior that exhibits a logarithmic divergence of the resistivity as the temperature approaches zero and (2) whereas the Hall coefficient typically measures the carrier concentration in a metal, we find that very small changes of the carrier concentration cause dramatic changes in the Hall coefficient. The data suggest the presence of a zero-temperature phase transition (a quantum critical point) precisely at the same carrier concentration at which high-temperature superconductivity is most stable--suggesting that a quantum critical point in the normal state phase diagram might well play an important role in the mechanism of high-temperature superconductivity--at least to the speaker and his co-authors.

This talk will be aimed at a general physics audience, both when discussing the magnet explosions and when discussing the condensed matter physics experiments that occur when the magnets don't explode.

***PLEASE NOTE CHANGE OF LOCATION FOR REFRESHMENTS!!***

David Dorfan
Physics Department, UC Santa Cruz

October 2, 2003

Presentation of demonstrations
from introductory physics courses &
New graduate student introductions
& state of the Department address

This week's Colloquium has been revised to include a presentation of demonstrations designed by Alex Helman and his students in the last twelve months. They cover introductory physics courses, the 5,6,7 series courses, and the quantum enigma. Accordingly refreshments will be served at 3:30 pm in THIMANN 2. Following the demonstrations, there will be a state of the Department address and introduction of new Physics graduate students. Alex has requested that people please arrive at 3:30 sharp.

Stan Woosley
Astronomy Department, UC Santa Cruz

0ctober 9, 2003

Gamma-Ray Bursts

Gamma-ray bursts are brief astronomical transients that come from random directions in the sky and glow very brightly in gamma-rays or hard x-rays. For thirty years, understanding their nature has been one of the greatest challenges facing high energy astrophysics. Recent evidence suggests that some of these events, now known to occur at cosmological distances, occur as one consequence of the death of a massive star. In the leading model, the "collapsar model," a black hole is born and fed matter at a prodigious rate by an accretion disk. The disk and hole produce a relativistic jet that exits the star and makes the burst. In the process, a bright radioactively-powered supernova is also created. Recent progress in the field of gamma-ray bursts will be reviewed with emphasis on the collapsar model.

Sean Carroll
University of Chicago

October 16, 2003

Dark Energy and the Preposterous Universe


A variety of observations have led cosmologists to conclude that the universe is dominated by a mysterious form of "dark energy" (in addition to the well-established "dark matter," which now seems prosaic by comparison). This dark energy could be vacuum energy (a cosmological constant), or something dynamical and slowly evolving. All of the possibilities are very exciting, and future observations have promise for distinguishing between them. I will give an overview of the theoretical proposals for dark energy and the observational constraints which any model must satisfy.

Shou-Cheng Zhang
Physics Department, Stanford University

October 23, 2003

Dissipationless Quantum Spin Current at Room Temperature


Although microscopic laws of physics are invariant under the reversal of the arrow of time, the transport of energy and information in most devices is an irreversible process. It is this irreversibility that leads to intrinsic dissipations in electronic devices and limits the possibility of quantum computation. We theoretically predict that the electric field can induce a substantial amount of dissipationless quantum spin current at room temperature, in hole-doped semiconductors such as Si, Ge, and GaAs. On the basis of a generalization of the quantum Hall effect, the predicted effect leads to efficient spin injection without the need for metallic ferromagnets. Principles found here could enable quantum spintronic devices with integrated information processing and storage units, operating with low power consumption and performing reversible quantum computation.

Gudrid Moortgat-Pick
Dept. of Physics, University of Durham,
United Kingdom

October 30, 2003

The Case for the Linear Collider


A world-wide consensus exists that a Linear Collider (LC) should be the next large experiment in high energy physics. In this talk the main capabilities of a LC with polarized beams are summarized. The physics arguments in favor of realizing such a machine as soon as possible are emphasized: the benefit of having overlapping running between the Large Hadron Collider (at CERN) and the LC, the prospects for new physics searches, as well as Standard Model high precision physics.

Matthew P.A. Fisher
Kavli Institute for Theoretical Physics
UC Santa Barbara

November 6, 2003

The Abnormal State of High Temperature Superconductors


Theoretical approaches to the cuprate superconductors broadly fall into two classes--one a force-fitting into the standard framework, and the other a quest for qualitative novelty. This talk will be firmly rooted in the latter. I will describe several exotic new quantum phases of 2D correlated electrons, and discuss their promise as candidate phases underlying the strange cuprate normal state behavior.

Yuval Grossman
Technion University
Haifa, Israel

November 13, 2003

Neutrino Masses


In recent years the experimental evidence that the neutrinos have tiny masses is mounting. We review the data and describe the theoretical motivations for small neutrino masses. In particular, we show how neutrinos probe the physics at very small distances.

Dung-Hai Lee
UC Berkeley

November 20, 2003

The mystery of Mott insulators


In this talk some of the unexpected physics in doped and undoped Mott insulators will be discussed.

NO COLLOQUIUM TODAY

THANKSGIVING HOLIDAY

November 27, 2003

Hans-Joachim Ziock
Los Alamos National Laboratory

December 4, 2003

CO2 Emissions: The Issue of Scale and Some New Approaches

Today world energy use and CO2 production is already well outside commonly considered scales, but nonetheless quite small in comparison to what is likely to come. These scales must be taken into account when examining possible future energy scenarios and when considering solutions to the carbon dioxide issue. In modern industrialized nations, CO2 emissions are about 20 tonnes per person per year; greater than any other commodity used, with the exceptions of water and air. Global yearly emissions are already more than 20 km3 at liquid densities, and this could grow by a factor of 10 this century and, in some sense, hopefully will. A world population of about 10 billion people enjoying the lifestyle and prosperity found in modern nations would require 10 times the energy using prevailing technologies. These issues of scale will be discussed as will be some new approaches for dealing with CO2 emissions resulting from the continued use of fossil energy. These include sequestration of CO2 in the form of mineral carbonates, direct extraction of CO2 from the atmosphere, and a zero-emission coal technology.

Please send suggestions for future speakers to the colloquium committee:
Howard Haber: haber@scipp.ucsc.edu
Sriram Shastry: sriram@bartok.ucsc.edu