Ivan Bozovic, OXXEL GmbH, Technologiepark Universitaet, Bremen D-28359, Germany

Presenting Author: I. Bozovic

A brief review will be given of the atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique and of its application to synthesis of HTS single-crystal films and heterostructures.

Success with ALL-MBE depends on one’s capability to accurately control absolute atomic fluxes and deposition rates, to monitor the chemical composition and the crystallographic structure of the surface layers and of the film, to observe the film morphology, and to control the mecha-nism(s) of nucleation and growth. Attempts are ongoing to advance these capabilities by integrating state-of-the-art surface-science tools with MBE systems, which permit in-situ, real time, quantita-tive studies of surface dynamics.

ALL-MBE enables fabrication of unique HTS samples. Single-phase HTS films can be synthe-sized even in the case when several competing phases are energetically almost degenerate. Novel ‘artificial’ HTS compounds have also been synthesized by virtue of atomic-layer deposition and/or epitaxial stabilization. Multilayers and superlattices have been grown with atomically perfect sur-faces and interfaces - e.g. between cuprates and manganites, allowing experiments that shed some light on intriguing HTS/CMR proximity effects. Also interesting are HTS/ferroelectric heter-ostructures, as well as the ‘long-range proximity effect’ between HTS and related compounds with a reduced T_c. Finally, the capability to deposit pinhole-free, ultrathin (down to one-unit-cell thick) barrier layers opens vistas for novel device concepts.

A. Yurgens and T. Claeson, Physics and Engineering Physics, Chalmers, 41296 Goteborg, Sweden

Presenting Author: T. Claeson

Pre-contacted, small mesas can be etched into a single crystal or an epitaxial film of a high temperature superconductor while the sample is cooled and transport measurements are performed during the etching process. The latter can be stopped at appropriate times, allowing detailed studies. Tunneling between superconducting planes occurs in the c-axis direction, resulting in so called intrinsic Josephson junctions. These can be applied, for example, to study current transport in the c-axis direction of Bi-2212 under magnetic fields in order to map vortex phase transitions and the irreversibility line, the vortex pinning by columnar defects from heavy ion irradiation, or the effects on the pseudogap and the superconducting interaction by changing the separations of the copper oxygen planes by intercalation or pressure. The properties and possible applications of intrinsic junctions as well as of the well studied grain boundary junctions will be discussed.

Tomoji Kawai, ISIR-Sanken, Osaka University, Mihogaoka, Ibaraki, 567-0047, Japan

Presenting Author: T. Kawai

This talk includes following topics.

1. BHTSC thin film formation using Laser MBE combined with RHEED and STM/AFM to characterize the growth process.

2. STM/STS measurements on the HTSC surfaces which demonstrate the characteristic electronic structures of highly correlated electron systems, not only for the Cu oxide systems but also for the Mn and Ni oxides systems.

3. Tunneling study of HTSC in the c-axis Josephson junctions between Nb and single crystal Bi₂Sr₂CaCu₂O₈ (BSCCO), and in the SN junctions using YBCO and Au thin films. The former experiment demonstrates the presence of an s-wave pairing state for the symmetry of order parameter in BSCCO, and the latter experiment examines the possibility of Andreev reflection above T_c in the pseudogap region. The results are discussed in termes of recent theoretical models of HTSC.