Electron correlations in the 2D multilayer organic metal _k63-(BEDT-TTF)_1tn2I_1tn3 [kappa-(BEDT-TTF) 2 I 3] in magnetic fields [Elektronische Ressource] / submitted by Eduard Balthes

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• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2004
• Nombre de lectures: 22
• Langue: English
• Poids de l'ouvrage: 5 Mo

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Electron Correlations in the 2D
Multilayer Organic Metal κ-(BEDT-TTF) I2 3
in Magnetic Fields
Habilitation
submitted by
Dr. Eduard Balthes
3. Physikalisches Institut
Universität Stuttgart
GermanyPreface
This work presents quantum oscillation experiments in quasi-twodimensional multilayer
organic metals. They show that low integer Landau level filling factors ν are present in the
two-dimensional organic metal κ-(BEDT-TTF) I and give strong indications for the2 3
existence of the fractional filling factor ν = ½ in this material. By this the work shows the
presence of electron localisation and electron correlation in a bulk metallic two-dimensional
system. These effects are found in the normal conducting state of the organic superconductor
κ-(BEDT-TTF) I .2 3
The revolutionary discovery of the integer as well as the fractional quantum Hall effect in
two-dimensional semiconducting single-layer systems invoked, i.a., the questions, whether
these effects may also be present in other types of conductors and, especially, whether they
may also occur in bulk three-dimensional crystals. Strong efforts were made to produce
bilayer two-dimensional semiconductors, to control their interlayer coupling as well as
electron tunnelling, to increase step by step the number of involved layers with the aim to
realise the quantised Hall effects in ‘bulk’ multilayer and, finally, in ‘infinite-layer’ systems.
Furthermore strong efforts are made in semiconducting two-dimensional systems to realise
11 2 7 2carrier densities above 10 /cm with mobilities exceeding 10 cm /Vs.
19 2κ-(BEDT-TTF) I is a metallic compound with a very high electron density of 2 10 /cm and2 3 *
8 2a very high carrier mobility reaching about 5 10 cm /Vs. From its structural principle this*
5organic material represents a system of 10 coupled metallic multilayers, which can be
synthesised in very high purity and can be produced as three-dimensional bulk single
crystals. Despite of this, the material shows strongly two-dimensional electronic properties
under certain experimental conditions, as found in the frame of this work. In contrast to the
characteristic situation in semiconducting two-dimensional systems, where (correlated)
electrons move on a single quantised orbit, the strongly correlated carriers in
κ-(BEDT-TTF) I move on various quantised orbits with even very different filling factors.2 3
These are the main conditions under which the above mentioned filling factors are found in
κ I . 2 3
Besides these characteristics, the present two-dimensional organic metal holds a number of
further peculiarities, which may represent a challenge for the understanding of possible
fractional filling factors and quantum limit in a macroscopic multilayer crystal with
two-dimensional electronic properties.
In addition, the present work resumes experiments on the influence of low-dimensionality
onto the electronic properties of a number of low-dimensional multilayer organic conductors.
Stuttgart, March 2004 Eduard Balthes
*
dedicated to Beate Baßfeld
IIContents
Preface II
List of Symbols and Abbreviations VII
1. Introduction 1
2. The Realisation of Two - Dimensional Electronic Systems 8
3. Electrons in Strong Magnetic Fields 14
3.1 Landau Quantisation and Magneto - Quantum Oscillations (QOs) 14
The de Haas-van Alphen (dHvA) Effect
3.2 Reduction of Quantum Oscillation Amplitudes by Phase Smearing 16
Effects
3.2.1 Finite Curvature of the Fermi Surface of a 3DES 16
3.2.2 Effect of Finite Temperature 17
3.2.3 Effect of Finite Relaxation Time 17
3.2.4 Effect of Electron Spin 18
3.3 The Shubnikov-de Haas (SdH) Effect 19
3.4 Departures From the Standard LK Theory for 3DES 21
3.4.1 Magnetic Interaction (MI) 21
3.4.2 Magnetic Breakdown (MB) 23
3.4.3 Effects of Quasi-Twodimensionality and Twodimensionality 27
of the System
• A Quasi-2D and 2D Fermi Surface (FS) in a Multilayer Metallic System 27
• Departures from the LK Formalism by a Warping of the FS 28
3.4.4 De Haas-van Alphen Effect in Two-Dimensional Electronic Systems 29
3.4.5 Influence of the Oscillating Chemical Potential on the Magnetic
Breakdown 31
3.4.6 Modification of the QO Spectrum in the MB Region by
Quantum Interference 32
3.4.7 Comparison of the Fourier Spectra in the Presence of MB,
an Oscillating Chemical Potential or QI 33
III4. The Quantised Hall Effects 38
4.1 The Integer Quantum Hall Effect (IQHE) 38
4.1.1 The Role of Localised States in the IQHE 41
4.1.2 Fundamental Difference Between Typical Semiconducting 2DESs
and 2D Organic Metals 41
4.1.3 Electron Localisation in the IQHE Regime - Microscopic Picture 43
4.1.4 The Role of Edge States in the IQHE 45
• The 1D Chiral Tomonaga-Luttinger Liquid 49
4.2 The Fractional Quantum Hall Effect (FQHE) 50
4.2.1 The Ground State 52
4.2.2 Laughlin’s Description of the ν = 1/3 Ground State 54
4.2.3 The Ground State Energy and the Energy Gap 55
4.2.4 Transition From a Laughlin Liquid to a Wigner Crystal at Low ν 56
4.2.5 Excited States: Quasiparticles and Their Main Properties 56
• Electron Localisation in the FQHE Region 58
• Fractional Statistics 58
• The Role of Impurities and Sample Inhomogeneities 59
• The Size of Quasiparticles - Localisation Lengths 59
4.2.6 Hierarchy of Higher Order Fractions: From ν = 1/m to ν = p/q 59
4.2.7 The Special Fraction ν = 1/2 in a Single-Layer 2DES:
Composite Fermions 62
4.2.8 The Special Filling Factors ν = ½ And ν = 1 in Multiple-Layer Systems 64
4.3 Other Results of Two-Dimensionality: Skyrmions 67
4.4 Interjection 70
5. Investigations of the 2D Multilayer Organic Metal κ-(BEDT-TTF) I 712 3
5.1 A Selection of General Electronic Properties of κ-(BEDT-TTF) I 722 3
• Crystal structure 72
• Resistivity Measurements on κ-(BEDT-TTF) I Single Crystals 732 3
• Thermopower Experiments at Zero Magnetic Field 74
• Superconducting Properties 75
5.2 Fermiological Studies on κ-(BEDT-TTF) I by Quantum2 3
Oscillation Experiments 76
5.2.1 Further Fermiological Properties of κ-(BEDT-TTF) I 822 3
• Magnetic Breakdown 82
• Electron g-Values, Dingle Temperatures T andD
Carrier Scattering Times τ 83
5.2.2 Quantification of the Two-Dimensionality 85
IV5.3 Strong Anomalies in the Quantum Oscillation Amplitudes
at High Fields, Low Temperatures and B ⊥ (b,c) ≡ Θ = 0°
as a Result of Two-Dimensionality 87
• Determination of the Carrier Effective Masses m* by Quantum
Oscillation Experiments 88
• Application and Limits of the Lifshitz-Kosevich Formula 89
5.3.1 Possible Reasons For the Anomalous Damping Effects of the
SdH Amplitudes of κ-(BEDT-TTF) I at High B Low T and Θ = 0° 932 3
• Spin Splitting and/or a Field Dependent g-Value 93
• Magnetic Interaction 94
• Magnetic Breakdown 95
• Warping 96
• Quantum Interference 96
• Further Possibilities: Superlattice and FS Instability 98
• Eddy Currents 98
• Theory of the dHvA Effect in 2D Systems 99
• Oscillation of the Chemical Potential with the QO Frequency F 1003
• Comparative dHvA and SdH Experiments at Θ = 0.07° 101
on the Same Crystal
• Interjection 103
5.3.2 The Very Special Experimental Conditions in a 2D Multilayer
Metal at Θ = 0° Compared to Θ ≠ 0° 104
5.4 The Role of the Low Frequency QO With F = 13T 1050
• Oscillation of the Chemical Potential with F 1100
5.5 The New Quantum Limit QO Frequency F = 3.8T 113new
• Could the Oscillations with F = 13T and F = 3.8T0 new
be Generated by Warping 115
5.6 Oscillations of the Chemical Potential With the Quantum Oscillation
Frequency F = 3.8T 118new
5.7 Connection Between the Damping Effects and the Filling Factors of F 118new
5.8 Indications for Fractional and Low Integer ν in the 2D Multilayer
Organic Metal κ-(BEDT-TTF) I and Its Consequences 1202 3
5.8.1 Coexistence of Extended and Localised States 122
5.8.2 Indications for Electron Localisation in κ-(BEDT-TTF) I Around 2 3
Fractional and Low Integer ν 122
5.8.3 Localisation Lengths 123
• Localisation Lengths Around Fractional ν 124Fnew
• Drift Lenghts in Magnetotransport 125
• The Discrepancy Between Results of dHvA and
SdH Experiments at High B Low T and 0° 125
V5.8.4 Questions on the Occurrence of Further Results
of Two-Dimensionality 126
• Edge States 126
• On the 1D Chiral Tomonaga-Luttinger Liquid 127
• Wigner Crystallisation 127
• Composite Fermions 128
• Skyrmions 128
5.8.5 Further Aspects and Open Questions 129
• Hall Effect Experiments 131
5.8.6 Provisional Appraisal 132
6. Search For Effects of Two-Dimensionality in Further Quasi-2D
Organic Metals 134
6.1 κ-Phase Organic Metals with Quasi-2D Electronic Properties 134
• κ-(BEDT-TTF) Cu(NCS) 1352 2
• κ Cu[N(CN) ]Br 1362 2
• κ ]Cl 1382 2
• κ-(BEDT-TTF) Ag(CN) H O 1382 2 2
• κ-(BEDT-TSF) Cu[N(CN) ]Br 1382 2
• κ C(CN) 1382 3
• κ-(DMET) AuBr 1392 2
6.2 Quasi-2D Organic Metals with Structures Different from κ-Phase 139
6.2.1 The Quasi-2D Organic Metal (BEDT-TTF) [Ni(dto) )] 1404 2
6.2.2 The Organic Charge-Transfer Salt
β”-(BEDT-TTF) SF CH CF SO 1432 5 2 2 3
6.2.3 The Quasi-Twodimensional α-Phase Salts
α-(BEDT-TTF)MHg(SCN) 1432 4
6.2.4 The Stable 8K Organic Superconductor