Low-Dimensional Molecular Metals

315 Pages·2007·6.601 MB·English

by  Professor Dr. Naoki Toyota, Dr. Jens Müller, Professor Dr. Michael Lang (auth.)

SpringerSeriesin
solid-state sciences
154
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Naoki Toyota
Michael Lang
Jens Müller
Low-Dimensional
Molecular Metals
With135Figuresand9Tables
123
ProfessorDr.NaokiToyota ProfessorDr.MichaelLang
TohokuUniversity,GraduateSchoolofScience UniversityofFrankfurt,FB13Physics
DepartmentofPhysics PhysikalischesInstitut
Aramaki Max-von-Laue-Str.1
980-8578Sendai,Japan 60438Frankfurt,Germany
E-mail:[email protected] E-mail:[email protected]
Dr.JensMüller
MaxPlanckInstitute
forChemicalPhysicsofSolids
NöthnitzerStr.40
01187Dresden,Germany
E-mail:[email protected]
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ProfessorDr.,Dres.h.c.Hans-JoachimQueisser
Max-Planck-Institutfu¨rFestko¨rperforschung,Heisenbergstrasse1,70569Stuttgart,Germany
∗Max-Planck-Institutfu¨rPhysikkomplexerSysteme,No¨thnitzerStrasse38
01187Dresden,Germany
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DepartmentofPhysics,5000EastUniversity,UniversityofMichigan
AnnArbor,MI48109-1120,USA
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To Kimiye, Mihoko, Naochika, Daiju
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Tina, Luke
Preface
Almost half a century has passed since the first molecular semiconductor
with a high electrical conductivity was found in 1954 in halogen-doped or-
ganiccomplexes.Thisfinding,coincidingwiththestructuralidentificationof
DNA, occurred seven years after the principle of a point-contact field-effect
transistor had been invented. Needless to say, these two outstanding inno-
vations of the 20th century have had great impact on the relevant fields of
science and technology. Similarly, though on a much smaller scale, the dis-
covery of organic semiconductors has set off in motion a large number of
elaborate works by chemists and physicists. In consequence, the researchar-
easoftodayhavedevelopedindepthandwidth,coveringfieldsrangingfrom
conducting polymers, liquid crystals, synthetic metals, molecular magnets,
molecular field-effect transistors to single-molecule devices and more.
This particular monograph is concerned with just one aspect of this vast
field, the physics of low-dimensional molecular metals (LDMM). This re-
search field has brought together groups from various disciplines such as
organic chemistry, physical chemistry, experimental physics, as well as theo-
retical chemistry and physics. The progress, which has been achieved in the
developmentofnewmaterialsandtheunderstandingoftheirexcitingproper-
ties, has been the result of intensive interactions among the members of this
interdisciplinaryclub.Onbehalfofthephysicsmembers,theauthors,allhav-
ing their roots in experimental physics, would like to appreciate the efforts
made by the chemical members, particularly, for exploring novel molecules
and crystals, otherwise such a club could not have existed.
The age of LDMM physics dawned around the early seventies when the
first molecular metal TTF-TCNQ, consisting of radical cation and anion
groups,was discovered.Their derivatives have been found to form many dif-
ferent charge-transfer salts with various kinds of radical molecules or metal
ions.Since then, anumber ofinterestinggroundstates andphasetransitions
has been observed: superconductivity, metal-insulator transitions associated
with charge- or spin-density-wave condensates, and other cooperative states
leadingtocharge-,antiferromagnetic-anddielectricorder.Aswellasinordi-
nary metals, all these phenomena are directly related both to the electronic
states near the Fermi level and to relevant interactions. An inherent ad-
vantage, particularly in LDMM, is due to the fact that the behavior of the
VIII Preface
conduction electrons, usually one or two carriers in large unit cells, can be
expressed surprisingly well by a simple tight-binding picture leading to sim-
ple Fermi surfaces (FS) which are being used in introductory textbooks for
low-dimensional electronic systems. This characteristic feature is unique for
LDMM and seen neither in ordinary bulk metals nor in compounds contain-
ing many complicated electron bands. During the last two decades, the FS
anditsrelatedphenomenahavebeenextensivelystudiedwiththeexperimen-
tal tools of low temperatures, and by applying magnetic fields and pressure.
Thusthe LDMMphysicsmayoccupyauniquepositioninsolidstatephysics
in such a way that physical phenomena can be more directly linked to the
experimentally clarified details of the electronic states.
With regard to contemporary solid state physics, the research era for
LDMM during the last three decades has overlapped with the enormous
progressmadeinotherfieldsofconductingmaterialsandtherelatedphysics:
for example, superconductivity and magnetism in heavy-fermion rare-earth-
based compounds, quantum Hall effect in artificial semiconductor hetero-
structures, high-T superconductivity in cuprates, supramolecular fullerene
c
C , andsuperconductivity in compounds with alkaline metals, metallic car-
60
bon nanotubes, to name only a few. On deliberating what these discoveries
have in common, we may find that the emergence of these new materials
has altered and sometimes overturns our common sense, familiar concepts,
or theories. This experience may be condensed into words uttered by H.
Kammerlingh Onnes: ”Door meten tot weten” (Through measurement to
knowledge).1
While keeping these notions in mind, this monograph intends to provide
an overview of LDMM physics including issues of controversy. The authors
refrained from including details of chemistry and theories, as these aspects
are outside the scope of their working fields. The intention of this book is to
describe the physics as plainly and systematically as possible for students at
graduate levels in solid state physics and chemistry courses with the back-
ground knowledge of introductory solid state physics/chemistry. The wide
spectrum of subjects addressed, together with the comprehensive list of ref-
erences, may be helpful even to experts in this field and also to researchers
working at the frontier of the other contemporary research areas mentioned
above.
Thismonographconsistsofsevenchapters.Chapter1willgiveanoverview
of the historical survey for molecular magnets and conductors. After a brief
introduction of the basic concepts for charge transfer and molecular orbitals
inChapt.2,thesystematicsofstructuralaspectscharacteristictoLDMMwill
be given in Chapt.3. Chapter4 will be concerned with the normal-metallic
stateswithcharacteristictransport,optical,thermal,magneticanddielectric
properties, and follow on to instabilities involving spin- and charge-degrees
1 K.Mendelssohn,The Quest for Absolute Zero,2ndedn.,Taylor&Francis,Lon-
don, 1977.
Preface IX
of freedom leading to spin- or charge-density-wave condensates, spin-Peierls
instabilitystates,andchargeordering.Intheremainingsections,many-body
effects andvarious phase diagramswill be described. Chapter5 will focus on
the effects of magnetic fields on conduction electrons, the so-called fermiol-
ogy, and field-induced electronic phase transitions and/or collective states.
The vast rangeof subjects concerning superconductivity will be described in
Chapt.6 covering the characteristic parameters, isotope labeling, the prob-
lem of disorder, superconducting vortex states, and pairing symmetry and
interaction. In Chapt.7, characteristicphenomena, causedby interactions of
conductionelectronswithlocalizedd-spinsexemplifiedinDCNQIandBETS
salts,willbe introduced.Afewwordswillbeaddedinthe Epiloguetouching
on important problems remaining to be solved and on the direction along
which the LDMM physics may trace its developments.
The authorswould like to express their sincere gratitude to Y. Muto and
T.Fukase,EmeritusProfessorsofTohokuUniversity(N.T.), the membersof
thecollaborativeresearchcenteratFrankfurtUniversity,Forschergruppe412
(M.L.), and S. vonMolna´r, Director of MARTECH and Professorof Physics
at Florida State University (J.M.).
Theauthorswishtothankmanycollaboratorsandcolleaguesforenlight-
ening discussions, exchange of ideas, or valuable advice: C. Akinci, H. Aoki,
A.Ardavan,S.Blundell,J.Brooks,A.Bru¨hl,E.Coronado,P.Day,M.Dres-
sel, S. Endo, R. Feyerherm, H. Fujiwara, U. Geiser, T. Goto, G. Gru¨ner, S.
Hill, Y.Iwasa,D.J´erome,S.Kagoshima,W.Kang,M.Kartsovnik,R.Kato,
S.Kawamata,A.Kini,H.Kobayashi,F.Kromer,C.Langhammer,A.Lebed,
K. Maki, H. Matsui, R. McKenzie, J. Merino, T. Mori, K. Murata,T. Naka-
mura,E. Negishi,Y. Nishio, Y. Noda, T. Nojima,T. Osada,V. Pashchenko,
B.Powell,K.Removic-Langer,L.Pintschovius,F.Pratt,G.Saito,T.Sasaki,
J.Schlueter,D.Schweitzer,J.Singleton,M.deSouza,F.Steglich,Ch.Strack,
S.Suellow,T.Sugimoto,U.Sushko,J.Suzumura,T.Suzuki,M.Tanatar,K.
Tanigaki, H. Tsuchiya, H. Uozaki, M. Watanabe, Y. Watanabe, B. Wolf, A.
Wolter, J. Wosnitza.
The authors would like to thank most warmly Carolyne Agnew for her
help in proof reading, Momoko Ishikawa and Atsumasa Hojo for their assis-
tance in revising figures and texts, John Schlueter, Masashi Watanabe and
TakehikoMoriforprovidingfiguresinChapts.1-3,andthepublisherforcon-
tinuous encouragement.
Sendai, Frankfurt, Tallahassee, Dresden Naoki Toyota
November 2006 Michael Lang
Jens Mu¨ller
Contents
List of Symbols and Abbreviations............................XIII
1 Introduction: Historical Remarks ......................... 1
2 Basic Concepts ........................................... 7
2.1 Charge Transfer........................................ 7
2.2 Molecular Orbitals and Transfer Integrals.................. 8
3 Structural Aspects........................................ 13
3.1 Molecular Building Blocks ............................... 13
3.2 Crystal Structures ...................................... 16
3.2.1 Quasi-One-Dimensional Compounds ................ 16
3.2.2 Quasi-Two-DimensionalCompounds ................ 19
3.2.3 Three-dimensional Compounds..................... 25
3.3 Anion Ordering and Glassy Phenomena ................... 29
4 Normal-State Properties.................................. 37
4.1 Tight-Binding Model.................................... 37
4.2 Fermi Surfaces and Low Dimensionality ................... 42
4.3 Electronic Properties.................................... 45
4.3.1 Transport and Optical Properties................... 45
4.3.2 Thermal and Magnetic Properties .................. 63
4.4 Instabilities Involving Spin- and Charge-Degrees of Freedom 75
4.4.1 Charge- and Spin-Density-Waves ................... 75
4.4.2 Spin-Peierls State ................................ 81
4.4.3 Charge-OrderingPhenomena ...................... 83
4.5 Many-Body Effects ..................................... 87
4.6 Phase Diagrams........................................ 91
5 Magnetic-Field Effects.................................... 99
5.1 Electron Motion in Magnetic Fields....................... 100
5.1.1 Semi-Classical Description in k-Space............... 100
5.1.2 Angular-Dependent Magnetoresistance Oscillations ... 101
5.1.3 Magneto-Optic Resonances ........................ 106
5.2 Magnetic Quantum Oscillations .......................... 109
5.2.1 Landau Levels and Lifshitz-Kosevich Theory......... 109
5.2.2 Magnetic Breakdown and Quantum Interference...... 117