ALSNews Vol. 221, April 30, 2003
ALSNews is a biweekly electronic newsletter to keep users and other interested parties informed about developments at the Advanced Light Source, a national user facility located at Lawrence Berkeley National Laboratory, University of California. To be placed on the mailing list, send your name and complete internet address to ALSNews@lbl.gov. We welcome suggestions for topics and content.
Previous Issues are available.
Table of Contents
- Campuzano Colloquium: Applying ARPES to Superconductivity
- First Call: General Sciences Proposals Due June 1
- Scientific Advisory Committee Convenes for Two-Day Session
- Congressional Delegation Tours ALS
- Operations Update
1. CAMPUZANO COLLOQUIUM: APPLYING ARPES TO SUPERCONDUCTIVITY
(Contact: ZHussain@lbl.gov)
"Breathtakingly beautiful experiments," was the reaction of one veteran practitioner of photoemission spectroscopy at the end of an ALS colloquium given by Juan Carlos Campuzano (University of Illinois at Chicago and Argonne National Laboratory) to a standing-room-only crowd on April 17. Campuzano's subject was the phase diagram of the high-temperature superconductors as seen by angle-resolved photoemission spectroscopy (ARPES). Campuzano's group has been one of the leaders in applying ARPES to the still-unanswered question of how high-temperature superconductors work, conducting its experiments at two different beamlines on the Aladdin storage ring of the University of Wisconsin Synchrotron Radiation Center. In his colloquium, Campuzano addressed two important boundaries in the phase diagram, which describes the ranges of temperature and composition within which the various phases (normal metal, superconductor, and so on) of these materials exist.
The most well known feature of the phase diagram is a dome-shaped region of superconductivity over a relatively small range of composition (doping) at low temperature. The superconducting phase transition in the low-doping (underdoped) composition range of high-temperature superconductors is rather unsual in that there is a pseudogap in the electronic excitation spectrum that appears at temperatures T* higher than Tc, while phase coherence and superconductivity are established at Tc. The first question Campuzano addressed was whether T* is just a crossover that is controlled by fluctuations in advance of an order that will be established at Tc or whether there is a spontaneously broken symmetry at T*. Using ARPES with circularly polarized light and a carefully controlled experiment geometry, Campuzano's group found that, in the pseudogap state, left circularly polarized photons result in a different photocurrent than right circularly polarized photons. The interpretation was that the state below T* breaks time-reversal symmetry. However, it remains unknown what the order is that is broken.
On the other hand, in the high-doping (overdoped) composition range, the group found evidence for a new crossover line in the phase diagram that divides a coherent metal phase (such as a normal Fermi liquid) at lower temperatures and higher doping from an incoherent metal phase (a strange metal) at higher temperatures and lower doping. For the composition corresponding to the top of the superconducitivity dome (optimally doped), the superconductor goes directly to the incoherent state upon being heated. The coherent phase is characterized by two well-defined spectral peaks in ARPES that are due to a coherent bilayer splitting, whereas the latter phase exhibits only a single broad spectral feature. To observe the crossover, the group had to "kill" the superconductivity by passing a current through the sample. This "flow-current" experiment tested the "pseudogap line" to see whether it terminates at the optimal doping or extends into the overdoped region. By flowing current to "kill" the superconductivity in the overdoped region, the researchers concluded that the pseudogap line extends to the overdoped region in Bi2212.
2. FIRST CALL: GENERAL SCIENCES PROPOSALS DUE
JUNE 1
(Contact: alsproposals@lbl.gov)
The User Services Office is now accepting general user proposals from scientists who wish to conduct research in the general sciences at the ALS during the running period from December 2003 to May 2004. The deadline for submissions is June 1, 2003. (This deadline does not apply to protein crystallography proposals, which have a separate process and schedule.)
Scientists wishing to renew a previous proposal must download the one-page "ALS Experiment Report and Request for Beamtime" form (see links below) and submit it to the User Services Office by the June 1 deadline. The form is in Rich Text Format (RTF) and can be saved to your hard disk, filled out, and attached in an email message to alsproposals@lbl.gov with the key words "Experiment Report" in the subject header. Proposals cannot be renewed for more than three cycles after they are first submitted. After three rollover cycles, a new proposal must be submitted. If your proposal is designated ALS-00799 or lower, then you must submit a new proposal to be eligible for beamtime.
The numeric rating for each proposal will be communicated to the user along with comments from the Proposal Study Panel, where appropriate. The cutoff rating for each beamline in the previous proposal cycle is published on the Web (see below). The following resources are available for further information:
ALS User Services Administrator
alsuser@lbl.gov
General user proposal process
http://www-als.lbl.gov/als/quickguide/independinvest.html
ALS General Sciences Proposal and Request for Beamtime
http://alsusweb.lbl.gov/4DCGI/WEB_GetForm/Page1P.shtml/Initialize
ALS Experiment Report and Request for Beamtime (renewal form)
http://www-als.lbl.gov/als/quickguide/expt_report.rtf
Beamline information
http://www-als.lbl.gov/als/als_users_bl/datasheets.html
http://www-als.lbl.gov/als/als_users_bl/bl_table.html
Proposal Study Panel (PSP) scores
http://www-als.lbl.gov/als/quickguide/pspscores.html
3. SCIENTIFIC ADVISORY COMMITTEE CONVENES FOR
TWO-DAY SESSION
(Contact: GLKrebs@lbl.gov)
The ALS Scientific Advisory Committee (SAC) addressed a wide range of topics during a recent two-day meeting held at the ALS on April 22 - 23. The SAC is charged with advising Berkeley Lab and ALS management on issues relating to ALS operations, resource allocation, and strategic planning. At this latest meeting, the SAC's agenda included several reports relating to the Department of Energy Office of Science's request for their advisory committees to establish subcommittees to consider what new or upgraded facilities will best serve Office of Science purposes over a time frame of the next 20 years. The advisory committees were then charged with providing reports that discuss the importance of the science that the facilites would support and the readiness of the facilities for construction. SAC member Sunil Sinha (Univ. of California, San Diego), co-chair of the Basic Energy Sciences Advisory Committee (BESAC) subcommittee, provided a briefing on the recommendations of his subcommittee. His counterpart from the Biological and Environmental Research Advisory Committee (BERAC) subcommittee, Janet Smith (Purdue Univ), also a member of the SAC, addressed the group via teleconference, summarizing her subcommittee's recommendations as they relate to x-ray light sources from the perspective of biology and environmental science. The SAC also heard about the three Berkeley Lab presentations: the ALS upgrade, CIRCE, and LUX.
Janos Kirz (Stony Brook Univ.), currently on sabbatical at the ALS, gave a talk on lensless imaging; Elke Arenholz (ALS) provided a status report on magnetic materials research; and Howard Padmore (Experimental Systems Group Leader), Nobumichi Tamura (ALS), and Ersan Ustundag (Caltech) updated the SAC on microdiffraction research at ALS beamlines. ALS Division Deputy for Science Neville Smith and SAC member Yves Idzerda (Montana State Univ. and chair of the ALS General Sciences Proposal Study Panel) led a discussion specifying procedures for the "Approved Program" mode of access. The meeting closed out with a discussion on actinide research and the benefits and risks of research involving hazardous materials (led by ALS Deputy Director Ben Feinberg, David Shuh of Berkeley Lab's Chemical Sciences Division, and John Joyce of Los Alamos National Laboratory). In attendance at this meeting were SAC members Samuel Bader (Argonne National Laboratory), James Berger (Univ. of California, Berkeley), Jennifer Doudna (Berkeley Lab), Yves Idzerda, Chair Stephen D. Kevan (Univ. of Oregon), Anders Nilsson (Stanford Synchrotron Radiation Laboratory/Stockholm Univ., Sweden), Sunil Sinha, Janet Smith, Donald. L. Sparks (University of Delaware), John Spence (Arizona State Univ.), Anthony Starace (Univ. of Nebraska-Lincoln), and Friso van der Veen (Paul Scherrer Institut).
4. CONGRESSIONAL DELEGATION TOURS ALS
Representative David Hobson (R-Ohio), the Chairman of the House Appropriations Subcommittee on Energy and Water Development--a key congressional panel for science funding--toured the ALS with two of his colleagues on April 25 as part of a larger visit to Bay Area national laboratories and water projects. Hobson, along with Rep. Marion Berry (D-Arkansas), and Rep. Michael Simpson (R-Idaho), met with senior Berkeley Lab management and heard about Lab programs such as advanced scientific computing (NERSC), the supernova satellite project (SNAP), and the Molecular Foundry. At the ALS, Director Daniel Chemla gave a brief introduction to how the ALS works, a few vital statistics, and a survey of future developments. The congressional delegation was then escorted to the experiment floor, where user Carolyn Larabell (Berkeley Lab's Life Sciences Division and the Univ. of California, San Francisco) gave an informal talk on how synchrotron light enables three-dimensional tomography of single cells. At Beamline 12.0.1, Erik Anderson, Ken Goldberg, and Patrick Naulleau (all of Berkeley Lab's Center for X-Ray Optics) described the implications for computer technology stemming from achievements in EUV lithography that have resulted from collaborations between three national laboratories and with industry. Hobson also stopped by a few workstations along the way and chatted with staff members Corie Ralston, Sue Bailey, Byron Freelon, and Yi-De Chuang about their work.
5. OPERATIONS UPDATE
(Contact: Lampo@lbl.gov)
The ALS was shut down for planned installations and maintenance on 8:00 P.M. on March 31, 2003. User operations were scheduled to resume at 8:00 A.M. this morning, Wednesday, April 30, 2003.
Long-term and weekly operations schedules are available on the Web (http://www-als.lbl.gov/als/schedules/index.html). Requests for special operations use of the "scrubbing" shift should be sent to Bruce Samuelson (ALS-CR@lbl.gov, x4738) by 1:00 p.m. Friday. The Accelerator Status Hotline at (510) 486-6766 (ext. 6766 from Lab phones) features a recorded message giving up-to-date information on the operational status of the accelerator. A Web page showing the ring status in real time can be found at http://www-als.lbl.gov/als/status/.
ALSNews is a biweekly electronic newsletter to keep users informed about developments at the Advanced Light Source, a national user facility located at Ernest Orlando Lawrence Berkeley National Laboratory, University of California. To be placed on the mailing list, send your email address to ALSNews@lbl.gov. We welcome suggestions for topics and content. Submissions are due the Friday before the issue date.
LBNL/PUB-875
Editors: lstamura@lbl.gov, alrobinson@lbl.gov, amgreiner@lbl.gov
This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.