A spin- and momentum-resolved photoemission study of strong electron correlation in Co/Cu(001) / Martin Ellguth.

Format:

Book

Thesis/Dissertation

Author/Creator:

Ellguth, Martin, 1984- author.

Language:

English

Subjects (All):

Photoemission.

Ferromagnetism.

Electron configuration.

Physical Description:

1 online resource (134 pages) : illustrations

Edition:

1st ed.

Place of Publication:

Berlin, Germany : Logos Verlag Berlin GmbH, [2015]

Summary:

Long description: Electron correlation is an important phenomenon of solid-state physics, which is actively studied both by experimentalists for the rich material properties which result from it and by theoreticians which face a lot of open questions on the way to a succesful many-body description of electron systems where the Coulomb interaction plays an important role. Ferromagnetic cobalt is an interesting candidate for the study of electron correlation, since the exchange interaction splits the band structure into majority-spin and minority-spin bands, which differ considerably in the strength of the electron-electron interaction.Using a revolutionary, parallelized approach to spin-resolved photoemission with an efficiency 3 to 4 orders of magnitude higher than previously possible, the spin-dependent manifestations of the electron correlation are revealed in unprecedented detail, allowing for a characterization of the self energy. As an additional phenomenon of the electron correlation, unusual waterfall features, previously only observed in superconductors, occur in the photoemission spectra of cobalt. Further subjects include a comprehensive mapping of the fcc cobalt Fermi surface and an investigation of unoccupied quantum well states in ultrathin cobalt films on copper accessed by spin-resolved, non-linear photoemission. The principle of the imaging spin filter and the data analysis routine are discussed in-depth in a dedicated chapter.

Contents:

Intro

1 Introduction

2 Theoretical background

2.1 The photoemission process

2.1.1 The free-electron final state model

2.2 Density functional theory and Local density approximation

2.3 Strongly correlated electron systems

2.4 Probing the spectral function A(~k,E) by photoemission

2.5 Spin-orbit coupling

2.5.1 Magnetic dichroism

2.6 Two-photon photoemission

2.7 Quantum well states in metallic thin films

3 Experimental methods

3.1 The momentum microscope

3.2 Electron spin detection principles

3.3 Spin-resolved photoemission measurements

3.3.1 Characterization of the imaging spin polarization analyzer

3.3.2 Evaluation of the spin polarization

3.3.3 Generation of an unpolarized electron image from Cu(001)

3.3.4 Analysis of the propagation of experimental errors

3.3.5 Time behaviour of the spin sensitivity of the W(100) crystal

3.4 Co thin films on Cu(001)

4 Measurements

4.1 Fermi surface of fct cobalt mapped by constant-initial state photoemission

4.1.1 Photon energy scan

4.1.2 Momentum distributions at discrete photon energies

4.2 Valence electronic structure of Co/Cu(001)

4.2.1 Valence electronic structure in the ΓWXK plane

4.2.2 Spin-resolved results

4.2.3 Exchange and spin-orbit contribution to the spin polarization

4.2.4 valence electronic structure in the WLWL plane

4.3 Beyond the bulk valence electronic structure

4.3.1 Final-state resonances

4.3.2 Surface resonances

4.4 Unoccupied electronic states probed by two-photon photoemission

4.4.1 Quantum well states in Co/Cu(001)

4.4.2 Dispersion and thickness dependence

4.4.3 Non-resonant two-photon processes versus one-photon processes

4.4.4 Spin polarization in resonant two-photon photoemission

4.4.5 Spin-orbit hybridization of majority and minority QWS

4.4.6 Conclusion.

5 Discussion

5.1 The complex band structure

5.2 Self-energy lifetime from photoemission linewidths

5.3 Strong versus weak correlation

6 Conclusion

7 Appendix

7.1 2D color code for spin-polarized images

7.2 Intensity asymmetries due to spin-orbit interaction

7.3 Asymmetry relations for off-normal photoemission (cubic (001) surface)

7.4 Point groups in the fcc (and fct) lattice

Bibliography

Publications

Acknowledgements.

Notes:

"Dissertation zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) der Naturwissenschaftlichen Fakultät II der Martin-Luther-Universität Halle-Wittenberg."

Ph.D. Martin-Luther-Universität Halle-Wittenberg 2015.

Includes bibliographical references (pages [107]-119).

Description based on print version record.

ISBN:

3-8325-8783-7

9783832587833