E-Book Content
FESTKÖRPER PROBLEMEXIII ADVANCES IN SOLIDSTATE PHYSICS Plenary Lectures of the Divisions "Semiconductor Physics", "Surface Physics", "Low Temperature Physics", "High Polymers", "Thermodynamics and Statistical Mechanics" of the German Physical Society Münster, March 19-24, 1973 Edited by H. J. Queisser, Stuttgart With 199 figures Pergamon Vieweg Pergamon Press Ltd., Headington Hill Hall, Oxford 0 X 3 OBW Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523 Pergamon of Canada L t d . , 207, Queen's Quay West, Toronto 1 , Canada Pergamon Press (Aust.) Ptv. L t d . , 19a Rushcutters Bay, Sydney, N.S.W. 2011 Friedr. Vieweg + Sohn G m b H , Burgplatz 1 , D-33 Braunschweig, Germany-West 1973 All rights reserved Copyright ©1973 by Friedr. Vieweg + Sohn GmbH, Verlag, Braunschweig Library of Congress Catalog Card No. 6 4 - 5 1 8 9 1 No part of this publication may be reproduced, stored in a retrieval system or transmitted, mechanical, photocopying, recording or otherwise, without prior permission of the copyright holder. Set by Friedr. Vieweg + Sohn GmbH, Braunschweig Printed by E. Hunold, Braunschweig Bookbinder: W. Langelüddecke, Braunschweig Cover design: Barbara Seebohm, Braunschweig Printed in Germany-West ISBN 0 08 0 1 7 2 9 3 8 Pergamon ISBN 3 528 0 8 0 1 9 1 Vieweg Foreword The elected chairman of the Semiconductor Division of the German Physical Society also serves as editor of this series. I took office as successor to O tfried Madelung, whom I sincerely thank for his many years of fruitful work. This volume contains once again a collection from the invited papers delivered at the joint spring meeting of the solid state divisions of the German Physical Society. The total number of plenary talks has risen so sharply that not all of them can be printed; the book would have become excessively voluminous. The necessary selection favors semiconductor physics, acknowledging the tradition of this series which began with Walter Schottky's editing. Surface phenomena are also stressed because there were joint sessions of the surface physics and semiconductor divisions at this meeting. International interest in this series naturally centered on articles written in English. It was therefore recommended to the authors that this language should be preferred from now on. Thus, all articles in this volume are in English. I thank the authors for this extra effort. I am also grateful to Vieweg-Pergamon for their now proverbially efficient and speedy publishing job. Hans-Joachim Queisser Münster, March 1973 Festkörperprobleme XIII (1973) Electronic Properties of Two Dimensional Solids: The Layer Type Transition Metal Dichalcogenides Abraham D. Yoffe Cavendish Laboratory, Cambridge Summary: This paper gives the results of recent experiments on the electrical, magnetic, opitcal and structural properties of layer type crystals. It deals in particular with the layer type transition metal dichalcogenides, MX2, and representative members are ZrS2, NbSe2, MoS2. These materials have been the subject of fairly intense activity during the past few years. It is argued that in NbSe2, there is a relatively narrow "d" band based on overlap of d| orbitals on the Nb atoms lying in the plane of the sandwich, and that it is this band which is the basis of many of the interesting physical properties, Phenomena such as excitons, screening effects, conduction in narrow "d" bands, superconductivity and the metal-insulator transtion are all encountered. Interaction of the MX2 crystals with a variety of organic and inorganic molecules and atoms can lead to quite dramatic changes in the physical properties. Long chain organic amines inserted between the MX2 layers in the van der Waal's gap can separate the layers by large di