Electron-Phonon Interaction in Conventional and Unconventional Superconductors (eBook)

Pegor Aynajian (Autor)

eBook Download: PDF

2011 | 2011
XII, 101 Seiten
Springer Berlin (Verlag)
978-3-642-14968-9 (ISBN)

Infos

The problem of conventional, low-temperature superconductivity has been regarded as solved since the seminal work of Bardeen, Cooper, and Schrieffer (BCS) more than 50 years ago. However, the theory does not allow accurate predictions of some of the most fundamental properties of a superconductor, including the superconducting energy gap on the Fermi surface. This thesis describes the development and scientific implementation of a new experimental method that puts this old problem into an entirely new light. The nominee has made major contributions to the development and implementation of a new experimental method that enhances the resolution of spectroscopic experiments on dispersive lattice-vibrational excitations (the 'glue' responsible for Cooper pairing of electrons in conventional superconductors) by more than two orders of magnitude. Using this method,he has discovered an unexpected relationship between the superconducting energy gap and the geometry of the Fermi surface in the normal state, both of which leave subtle imprints in the lattice vibrations that could not be resolved by conventional spectroscopic methods. He has confirmed this relationship on two elemental superconductors and on a series of metallic alloys. This indicates that a mechanism qualitatively beyond the standard BCS theory determines the magnitude and anisotropy of the superconducting gap.

Inhalt

Electron–Phonon Interaction in Conventional and Unconventional Superconductors 3
Supervisor’s Foreword 6
Acknowledgement 8
Contents 10
1 Introduction 12
1.1…History of Superconductivity 12
1.2…Neutron Spectroscopy of Superconductors 14
References 16
2 Phonons and Their Interactions 18
2.1…The Phonon--Phonon Interaction 18
2.2…The Electron--Phonon Interaction 20
2.2.1 Kohn Anomalies in the Phonon Dispersion of Metals 22
References 24
3 Conventional Superconductivity 25
3.1…Overview of the Microscopic Theory of Superconductivity 25
3.1.1 The BCS Formalism 25
3.1.2 The Eliashberg Formalism 27
3.2…Experimental Approach to the Electron--Phonon Interaction and Superconductivity 28
3.3…Anisotropy of the Superconducting Energy Gap 29
References 33
4 Unconventional Superconductivity 34
4.1…Phenomenology of Cuprates 34
4.1.1 Insulating Regime 35
4.1.2 Metallic Regime 36
4.1.3 Strange Metal Phase 36
4.1.4 Pseudogap 36
4.2…Proposed Theories of High Tc Superconductors 37
4.2.1 Phonon-Mediated HTSC 37
4.2.2 RVB Approach 37
4.2.3 Spin Fluctuations 38
4.2.4 Inhomogeneity-Induced Pairing 38
4.3…Experimental Overview of the Normal and Superconducting Gaps in Cuprates 38
4.4…Importance of the Electron--Phonon Interaction in HTSC 42
References 46
5 Neutron Spectroscopy 48
5.1…Triple-Axis Spectroscopy 48
5.2…Neutron Spin Echo Spectroscopy 50
5.3…Neutron Resonance Spin Echo for Dispersive Excitations 51
5.4…Neutron Resonance Spin Echo for Larmor Diffraction 53
5.5…NRSE-TAS Spectrometer TRISP at FRM-2 55
References 57
6 Experimental Aspects 58
6.1…Experimental Details 58
6.2…Samples 60
6.3…The NRSE-TAS Resolution Function 64
6.3.1 Instrumental Resolution 65
6.3.2 Sample Mosaic Spread 66
6.3.3 Curvature of the Phonon Dispersion Surface 66
6.3.3.1 Phonon Dispersion Surface 67
6.3.3.2 Nb 69
6.3.3.3 LSCO 70
6.4…Data analysis and Correction 71
References 74
7 Results and Discussion 75
7.1…Conventional Superconductors 75
7.1.1 Niobium 76
7.1.2 Lead 80
7.1.3 Lead--Bismuth Alloys 89
7.1.4 Transition Metal Dichalcogenide 2HminusNbSe2 91
7.2…High Temperature Superconductor LSCO 95
References 103
8 Conclusion 105
References 106
Vita 108

Produkt-Details

• Erscheint lt. Verlag: 19.1.2011
• Reihe/Serie: Springer Theses
• Reihe/Serie: Springer Theses
• Zusatzinfo: XII, 101 p.
• Verlagsort: Berlin
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Maschinenbau
• Schlagworte: Electron-phonon interaction • Kohn Anomaly • Neutron Resonance Spin Echo Spectroscopy • neutron scattering • Superconductivity
• ISBN-10: 3-642-14968-5 / 3642149685
• ISBN-13: 978-3-642-14968-9 / 9783642149689