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FESTKORPERPROBLEME ADVANCES IN SOLID STATE PHYSICS 31 FESTK()RPER PROBLEME ADVANCES IN SOLID STATE PHYSICS 31 Plenary Lectures of the Divisions Semiconductor Physics Thin Films Dynamics and Statistical Physics Magnetism Metal Physics Surface Physics Low Temperature Physics of the German Physical Society (DPG), M~nster, April 8 to 12, 1991 Edited by Ulrich R6ssler vleweg Editor: Prof. Dr. Ulrich R6ssler Institut tVtir Theoretische Physik Universit~it Regensburg P.O. Box 397 D-8400 Regensburg, F R G Die Deutsche Bibliothek - CIP-Einheitsaufnahme Festkiirper-Probleme = Advances in solid state physics. Braunschweig; Wiesbaden: Vieweg, 1991 Bis Bd. 15 (1975) aul]erdem im Verl. Pergamon Press, Oxford, Elmsford, T o r o n t o , Sydney ISSN 0430-3393 NE: P T 31. Plenary lectures of the Divisions Semiconductor Physics ... of the German Physical Society (DPG): Mt~nster, April 8 t o 12, 1991. - 1991 ISBN 3-528-08039-6 NE: Deutsche Physikalische Gesellschaft / FachausschuB Halbleiterphysik Vieweg i¢ a subsidiary company of the Bertelsmann Publishing G r o u p International. All rights reserved © Friedr. Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig 1991 No part of this publication may be reproduced, stored in a retrieval system or transmitted, mechanical, by photocopying or otherwise, without prior permission of the copyright holder. Printed by Lengericher Handelsdruckerei, Lengerich Bound by Hunke + Schr6der, Iserlohn Cover design: Barbara Seebohm, Braunschwejz_ Printed on acid-free paper Printed in the Federal Republic of Germany ISSN 04030-3393 ISBN 3-528-08039-6 Preface The annual conference 1991 of the Solid State Physics Division (Arbeitskreis FestkOrperphysik) was held together with the 55th General Meeting of the German Physical Society inMUnster. This volume contains a selection of plenary and invited talksdevoted t o the physics of solids, which have been presented during this conference. Some emphasis is put on two groups of topics: surface and interface properties and lowdimensional semiconductor structures. The former demonstrates the capability of different experimental techniques of anatomicscale resolution and an improved understanding of hetero-interfaces in combination with a microscopic theoretical description. The latter covers optical and transport studies of confined electrons. Two contributions are related t o phonons in high-Tc superconductors: their detection by Raman scattering (by Ch. Thomsen,the recipient of the Walter-Schottky prize 1991) and the relevance for superconductivity of their coupling with electrons. Transport in amorphous solids and ffactal systems, spectroscopic characterization of thin layers, laser diodes for optical communication, time-resolved spectroscopy and nonlinear properties of excitons, dilute magnetic semiconductors in strongmagnetic fields, and transport of hot electrons complete the wide spectrum of topics. The authors of this volume have been requested to deliver camera-ready manuscripts. Slight inhomogeneities due to different text processing systems have been tolerated in order to keep the production costs as low as possible. The ever good cooperation with BjOrn Gondesen from the Vieweg publishing househelped to make the work for this volume an easy one. Regensburg, May 1991 Ulrich R6ssler Contents Christian Thornsen R a m a n Scattering in H i g h - Tc Superconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Roland Zeyher H o w R e l e v a n t is the Electron-Phonon Coupling in H i g h - Tc Superconductors? . . . 19 Walter Schirmacher and Michael Wagener A n o m a l o u s Diffusion and A n o m a l o u s S o u n d Propagation in A m o r p h o u s Solids . 39 Gilnter Dumpich A n o m a l o