a Study of Correlation Effects - Archive ouverte UNIGE

UNIVERSITÉ DE GENÈVE FACULTÉ DES SCIENCES
Département de physique Professeur J.-M. Triscone
de la matière condensée
Transport Properties of
LaTiO3+δand REBa2Cu3O7−δ
Thin Films:
a Study of Correlation Effects
THÈSE
présentée à la Faculté des sciences de l’Université de Genève
pour obtenir le grade de docteur ès sciences, mention physique
par
Stefano GARIGLIO
de
Gênes (Italie)
Thèse n◦3419
GENÈVE
Atelier de Reproduction de la Section de Physique
2003

Contents
Résumé en français vii
R.1 Introduction ................................. vii
R.2 Effet de champ ferroélectrique ....................... viii
R.2.1 Modulation de la supraconductivité ................ ix
R.2.2 Modulation de Tc.......................... x
R.2.3 Transition supraconducteur-isolant ................. xi
R.2.4 Modulation des propriétés dans l’état normal ........... xi
R.3 Couches minces de LaTiO3+δ........................ xiv
Introduction 1
Main goal of the Thesis .............................. 2
Outline of the Thesis ............................... 3
1 Electron correlations in solids 5
1.1 Metal-insulator transition .......................... 5
1.2 Mott insulator ................................ 6
1.3 Hubbard model ............................... 6
1.4 Slater’s theory of Mott insulators ...................... 8
1.5 MIT phase diagram ............................. 9
1.6 Polarons ................................... 10
1.7 Anomalous metallic phases ......................... 11
1.8 High-Tcsuperconductors .......................... 11
1.8.1 Crystal and electronic structure .................. 12
1.8.2 Phase diagram ........................... 13
i

ii Contents
1.9 LaTiO3: structure and phase diagram .................... 14
2 Experimental set-up 17
2.1 Thin film deposition ............................. 17
2.1.1 Sputtering .............................. 18
2.1.2 Molecular Beam Epitaxy ...................... 19
2.2 Structural analysis of thin films ....................... 20
2.2.1 X-ray analyses ........................... 20
2.2.2 Transmission Electron Microscopy ................ 22
2.3 Lithographic patterning ........................... 23
2.4 Transport measurements: resistivity and Hall effect ............ 23
3 Ferroelectric Field Effect in thin superconducting films 25
3.1 Ferroelectric Field Effect .......................... 25
3.2 High-Temperature Superconductivity .................... 26
3.2.1 The polaron-bipolaron model ................... 27
3.2.2 The spin fluctuation scenario .................... 28
3.3 Ferroelectricity ............................... 29
3.3.1 Sawyer-Tower circuit ........................ 30
3.4 Ferroelectric Field Effect Devices ..................... 31
3.5 Thin Film Growth and Characterization .................. 33
3.5.1 Cuprate growth ........................... 33
3.5.2 Finite size effect in High-Tcthin films ............... 34
3.5.3 PZT thin films ........................... 37
3.6 Modulation of Superconductivity ...................... 39
3.6.1 PZT/GBCO/PBCO heterostructures ................ 39
3.6.2 P−Eand R−Eloops ...................... 39
3.6.3 Shift of Tc.............................. 40
3.6.4 Superconductor-insulator transition ................ 42
3.7 Modulation of Normal State Properties ................... 48
3.7.1 PZT/NBCO heterostructures .................... 48

Contents iii
3.7.2 Lithographic patterning of FFE heterostructures .......... 49
3.7.3 Local ferroelectric poling ...................... 50
3.7.4 Resistance and Hall modulation .................. 51
3.7.5 Variable versus fixed carrier density ................ 52
3.7.6 Anderson localization of bipolarons ................ 54
3.7.7 Two scattering times model .................... 55
3.7.8 Implication of the modulation of the normal state properties . . . 55
4 LaTiO3+δthin films: growth and transport properties 61
4.1 Growth of LaTiO3+δthin films ....................... 62
4.2 Structural analysis .............................. 64
4.3 Transport properties for films prepared on (001) LAO substrates ..... 68
4.3.1 Transport mechanism ........................ 70
4.4 Films prepared on (001) STO substrates .................. 74
Conclusions 77
Acknowledgements 79
References 81