Chemistry and Physics of One-Dimensional Metals

425 Pages·1977·17.047 MB·English

by  V. J. Emery (auth.), Heimo J. Keller (eds.)

Chemistry and Physics of
One-Dimensional Metals
NATO ADVANCED STUDY INSTITUTES SERIES
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Series B: Physics
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Volume 24 - Electrons in Finite and Infinite Structures
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Volume 25 - Chemistry and Physics of One-Dimensional Metals
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Chemistry and Physics of
One-Dimensional Metals
Edited by
Heimo 1. Keller
Anorganisch-Chemisches Institut der Universitiit
Heidelberg, Germany
PLENUM PRESS. NEW YORK AND LONDON
Published in cooperation with NATO Scientific Affairs Division
Library of Congress Cataloging in Publication Data
Nato Advanced Study Institute on Chemistry and Physics of One-Dimensional Metals,
Bolzimo (City), 1976.
Chemistry and physics of one-dimensional metals.
(NATO Advanced study institutes series: Series B, Physics; v. 25)
"Published in cooperation with NATO Scientific Affairs Division."
Includes index.
1. One-dimensional conductors-Congresses. 2. Organometallic compounds-Con-
gresses. I. Keller, Heimo 1., 1935- II. North Atlantic Treaty Organization.
Division of Scientific Affairs. III. Title. IV. Series.
QCI76.8.E4N33 1976 530.4 77-5135
ISBN 978-1-4615-8917-4 ISBN 978-1-4615-8915-0 (eBook)
DOl 10.1007/978-1-4615-8915-0
Lectures presented at the NATO Advanced Study Institute on Chemistry and Physics
of One-Dimensional Metals held in Bolzano, Italy, August 17-29, 1976
© 1977 Plenum Press, New York
Softcover reprint of the hardcover 1st edition 1977
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PRE F ACE
Theoretical and experimental work on sol ids with low-dimensio
nal cooperative phenomena has mushroomed in the last few years, and
it seems to be quite fashionable to contribute to this field,
especially to the problem of one-dimensional metals. The huqe amount
of recent investigations on quasi one-dimensional metals could be
divided into two parts although there is much overlap between these
regimes, namely investigations on orqanic materials such as TTF
TCNQ and its derivatives or the TTT halides, and secondly research
on inorganic sol ids with the highly conducting polymer (SN)x and
transition metal complexes 1 ike KCP, platinum oxa1ates or the mixed
valence dicarbony1ha10iridates. There is, of course, much over1ao
between these fields and in some cases theories have been tested on
both types of compounds simultaneously. In fact, however, most of
the scientific groups in this area could be associated roughly with
one of these categories and, in addition, a separation between
theoreticians and experimental ists in each of these groups leads to
a further sp1 itting of interests. Furthermore, the small number of
compounds studied thoroughly so far suggests an "information gap"
between chemists and physicists which hampers the testinq of new
materials. More cooperation and understanding between scientists
working on quasi ld conductors should appreci·ab1y stimulate further
development. With a better interdiscip1 inary understanding, new
ideas could possibly help chemists in synthesizing tailor-made
sol ids. This would in return give experimental ists new ohenomena to
examine and finally would stimulate new theoretical work.
It was the purpose of the NATO ASI held in Bo1zano, Italy, to
stimulate this cooperation and to develop a common 11anguage", which
means that the theoretical background of 501 id state physics of
extremely anisotropic 501 ids would be taught from the beginninq to
chemists and experimental physicists. Furthermore, the experimental
physicists gave a detailed account of what they had done on "meta1-
1 ic" ld sol ids and what type of experiments could be done in the
future, together with a mention of technical app1 ication of these
ideas. Finally, the preparative chemists gave an up-to-date summary
of the progress made in this field reqardinq the preparation of
v
PREFACE
tailor-made molecules and indicated what kind of compounds could
be prepared in the near future.
In several evening and weekend sessions some participants
presented summaries of their recent work and these and other new
results were discussed. A draft of these discussions could not be
added in printed form because of the 1 imitations set by the total
page number of this volume, but to give at least an idea of the
problems touched upon during these sessions, a 1 ist of the main
contributors together with the title of the conribution discussed
is given as an appendix. The reader might contact these authors
directly if interested in special recent results.
I hope that the participants have profited from the meeting
and, furthermore, that at least some of the readers of the following
papers are stimulated to high-dimensional cooperative efforts on
low-dimensional conductive sol ids.
Primarily I have to thank NATO who made this project possible
through generous financial support. Especially I would 1 ike to men
tion gratefully the excellent cooperation with Dr. T. Kester of the
NATO Scientific Affairs Division, whose personal efforts helped in
the preparation and organization of the meeting. The Advanced Study
Institute could not have taken place without the efforts of Mrs.
G. Egerland who did all the correspondence, the typing of particu
lars and most of the book-keeping. In addition the
or~anizational
work of the Co-directors, Dr. D. Nathe and Dr. H. Endres is thank
fully acknowledged. The generosity of IBM Germany and National
Science Foundation travel grants awarded to three US-participants
contributed to the completeness of the school.
Heimo J. Keller
Heidelberg
November 1976
CON TEN T S
The Basic Physics of One-Dimensional Metals
V. J. Emery
The Organic Metallic State: Some Chemical Aspects 25
D. Cowan, P. Shu, C. Hu, W. Krug,
T. Carruthers, T. Poehler, and A. Bloch
The Organic Metallic State: Some Physical Aspects
and Chemical Trends ..... 47
A. N. Bloch, T. F. Carruthers, T. O. Poehler,
and D. O. Cowan
Charge Density Wave Phenomena in TTF-TCNQ and
Related Organic Conductors ..... 87
A. J. Heeger
The Role of Coulomb Interactions in TTF-TCNQ 137
J. B. Torrance
Electronic Properties of the Superconducting
Polymer (SN)x .•........ 167
R. L. Greene and G. B. Street
Collective States in Single and Mixed Valence
Metal Chain Compounds ...... . 197
P. Day
The Structure of Linear Chain Transition Metal
Compounds with ld Metallic Properties 225
K. Krogmann
The Chemistry of Anisotropic Organic Materials. . . . . .. 233
F. Wudl
Superconductivity and Superconducting Fluctuations. . . .. 257
W. A. Little
viii CONTENTS
Instabil ities in One-Dimensional Metals 267
H. Gutfreund
Physical Considerations and Model Calculations
for One-Dimensional Superconductivity 279
H. Gutfreund and W. A. Little
Organic Linear Polymers with Conjugated Double Bonds. .. 297
G. Wegner
X-Ray and Neutron Scattering Investigations of
the Charge Density Waves in TTF-TCNQ 315
R. Comes
Electronic Properties of Organic Conductors:
Pressure Effects . . . . . . 341
D. Jerome and M. Weger
Charge Density Waves in Layered Compounds
F. J. Di Sa 1v o
Comparison of Columnar Organic and Inorganic
So 1 ids . •.•....... 391
Z. G. Soos and H. J. Keller
Append i x • . • . . . • . • . • . . . . . . . . . . . . .. 413
Subject Index 415
THE BASIC PHYSICS OF ONE-DIMENSIONAL METALS*
v. J. Emery
Department of Physics, Brookhaven National Laboratory
Upton, NY 11973
I. INTRODUCTION
The study of nearly one-dimensional metals has reached an
interesting stage of development. In the past few years there have
been so many advances in theory and experiment that we are just
about at a point where it is possible to understand much of what is
going on in particular materials or at least to plan a rational
program to find out. Of course there are many problems to solve
and different points of view to reconcile, but this makes it an all
the more appropriate time to hold a NATO Advanced Study Institute
at which many of these questions can be described and explored.
These introductory lectures will give a qualitative description of
the physical concepts upon which our present understanding of such
systems is based. They will be largely non-mathematical, leaving
the details to be found in the original papers or in other lectures
at this Institute.
Nearly one-dimensional metals are characterised by their very
anistropic properties, exemplified by the electrical conductivity
which takes place almost entirely along one particular direction.
This behaviour is a consequence of their structure - the molecules
or ions are typically arranged in chains or stacks along which the
electrons move rather easily, whereas motion in a perpendicular
direction is more difficult because it involves a "hopping" over
relatively large intermolecular distances. The Physicist's inter
est in this field stems largely from the opportunity to study an
almost one-dimensional electron gas, which has many characteristic
and unusual properties. It has been spurred by the prospect of
finding high temperature superconductivity I or at least an unusually
high conductivity produced by some collective mechanism, and much
2 V. J. EMERY
of the discussion at this Institute will be concerned with this
idea.
The structures of particular materials will be described in
detail in succeeding lectures and, for the present, it will be
sufficient to use a relatively simple model in terms of which the
physical properties may be discussed. It is assumed that each
molecular site has only one spatial state for a conduction electron.
The exclusion principle then allows at most two electrons (one of
each spin) to occupy a single site. This assumption simplifies the
argument and is justified when the spacing of electronic levels on
a particular molecule is larger than the other energies in the
problem, so excited states may be ignored. To draw a clearer dis
tinction between the various physical effects, it will be assumed
at first that the molecules form a rigid lattice,and discussion of
the very important role of phonons will be deferred until later.
Then the system is specified by the following parameters:
amplitude for hopping from site to site along the
chain
t.L amplitude for hopping from chain to chain
U interaction energy between electrons on the same
molecular site
V.u - interaction between an electron on site i and an
i.
electron on site
In a nearly one-dimensional material, til »t.Lo It may also be
~hat V!l is largest for two sites within the same chain, but that
1S not necessary. The magnitudes of these quantities will be dis
cussed material by material in the later lectures but, for values
to keep in mind, it is estimated that in TTF-TCNQ, til is about
0.1 eVand (t.L/tll) ~ 0.05. There is more uncertainty about u.
Coulomb interactfons make U > 0 but they are diminished by delocal
isation of electrons within a molecule and opposed by an effective
electron-electron interaction due to polarisation of the molecule
that could conceivably be large enough to make U negative. At
present there is no universal agreement about the outcome of this
competition in many of the interesting materials, and several of
the lectures will be concerned with what the current experiments
have to tell us about it. The most significant connection between
the chains is provided by Vi'. It is mainly a Coulomb interaction,
although there is also a co~ribution from electron-phonon coupling.
Much of the physics of almost one-dimensional metals is con
cerned with understanding the conditions for various kinds of phase
transitions which lead to collective states governing the low temp
erature behaviour. This is of central importance in the search
for high temperature superconductivity which, for example, could be