Study of superconductors using microscopic arrays of GaAs/AIGaAs 2 DEG Hall sensors

• Forschungsstelle: EU FRP
• Projektnummer: 01.0042
• Projekttitel Englisch: Study of superconductors using microscopic arrays of GaAs/AIGaAs 2 DEG Hall sensors

Schlüsselwörter (Englisch)

Superconductivity; vortex matter

Alternative Projektnummern (Englisch)

EU project number: HPRI-CT-00069

Forschungsprogramme (Englisch)

EU-programme: 5. Frame Research Programme - 4.2 Agriculture and agroindustry

Kurzbeschreibung (Englisch)

See abstract

Partner und Internationale Organisationen (Englisch)

Coordinator: Weizmann Institute of Science, Rehovot (IL)

Abstract (Englisch)

DURING THE PAST YEAR THREE SCIENTIFIC VISITS (13.3-27.3, 11.5-27.5, 20.12-27.12) TO THE WEIZMANN INSTITUTE OF SCIENCE WERE MADE. DURING THE FIRST TWO VISITS IN SPRING I GAVE ADVANCED LECTURE COURSE ON SUPERCONDUCTIVITY. THIS WAS THE JOINT COURSE WITH PROF. Y. IMRY FROM THE WEIZMANN INSTITUTE. IN MAY I PARTICIPATED IN THE MINERVA-ISF CONFERENCE ON HIGH TEMPEREATURE SUPERCONDUCTIVITY. THE MAIN PURPOSE OF THESE VISITS WAS JOINT RESEARCH WITH PROF. E. ZELDOV AND HIS GROUP ON THE PHASE TRANSITIONS IN THE VORTEX MATTER. ONE OF THE MOST INTRESTING EXPERIMENTAL RESULTS WHICH THEY OBTAIN (AVRAHAM N. ET AL. NATURE 411 (6836): 451-454, 2001) WAS THE FINDING THAT THE SO CALLED SECOND PEAK EFFECT APPEARS AS A FIRST ORDER TRANSITION. THE LINE OF THIS TRANSFORMATION GOES SMOOTHLY TO THE FIRST ORDER MELTING TRANSITION. THESE RESULTS WERE OBTAINED BY EXTENDING THE ``SHAKING'' TECHNIQUE, WHICH WAS DEVELOPED IN ZURICH IN THE JOINT COLLABORATION OF THE UNIVERSITY (GROUP OF PROF. H. KELLER) AND THE IBM - RUSCHLIKON (DR. C. ROSSEL GROUP), WILLEMIN M. PHYS. REV. LETT. 81, 4236 (1998). THEY FOUND THAT MAGNETIC IRREVERSIBILITY OF VORTEX MATTER CAN BE SUPPRESSED BY APPLYING A WEAK TRANSVERSE AC MAGNETIC FIELD. THE WEIZMANN GROUP USED THIS TECHNIQUE FOR THEIR STUDY OF BSCCO. BY THIS ``SHAKING'' THEY WERE ABLE TO SUPPRESS THE PEAK EFFECT AND TO SEE THE JUMP IN REVERSIBLE MAGNETIZATION WHICH IS A SIGNATURE OF THE FIRST ORDER MELTING TRANSITION. ALTHOUGH THIS ``AC SHAKING'' EFFECT SEEMS TO BE VERY POWERFUL TOOL TO SUPPRESS IRREVERSIBILITY THE THEORETICAL UNDERSTANDING OF IT IS STILL LACKING. DURING MY VISIT WE DEVELOPED A MODEL FOR THIS PHENOMENON. DURING THE AC CICLE JOSEPHSON VORTICES PENETRATE THE SAMPLE. THEY PRODUCE AC CURRENT THAT ACTS ON THE ABRIKOSOV VORTICES. THIS AC CURRENT HELPS VORTICES TO OVERCOME THE PINNING BARRIERS THUS ENHANCING CREEP AND REDUCING IRREVERSIBILITY. IN THIS MODEL IT APPEARS THAT THE AC TRANSVERSE CURRENT IS MORE EFFECTIVE THAN THE DC ONE SINCE IN EACH CICLE
IT PRODUCES SOME VORTEX MOTION. ANOTHER PART OF OUR COLLABORATION WAS RELATED WITH THE EFFECT OF THE COLUMNAR TRAPS ON THE FIRST ORDER MELTING TRANSITON. COLUMNAR TRAPS PRODUCE THE UPWARDS SHIFT OF THE MELTING LINE. IT WAS ALSO FOUND THEY CHANGE THE ORDER OF TRANSITION FROM THE FIRST ORDER TO THE CONTINUOUS ONE.

Datenbankreferenzen (Englisch)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 01.0042