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| Calendar: | ALS Calendar |
| Title: | ALS Special Seminar | TeYu Chien |
| When: | 10/16/2012 10:00 AM - 11:00 AM |
| Description: | ALS Special Seminar Tue, Oct 16, 2012 10 - 11am 6-2202 Host: Eli Rotenberg Presented by: TeYu Chien Department of Materials Science and Engineering, Northwestern University Title: Electron-Phonon Coupling in a system with broken symmetry: Surface of Be(0001) Abstract: The electron-boson coupling (EBC) is a many-body physics that governs many physical properties in novel materials, such as superconductivity. In general, EBC alters the self-energy of the electron/quasiparticle and renormalize the electronic dispersion relation near Fermi energy. By using angle-resolved photoemission spectroscopy (ARPES), the band renormalization near Fermi energy due to EBC could be studied in details and the underlying mechanism could be further discussed. For examples, the kink features found in the cuprate electron band dispersion were studied intensively in order to obtain insight of the origin of superconductivity, which is believed to be the result of EBC. However, up-to-date, the relationship between ARPES data and the coupled boson modes are not clearly demonstrated yet. Toward this goal, here, we utilize ARPES to investigate electron-phonon coupling (EPC) on an isotropic, free-electron-like 2D electronic band structure system – Be(0001) Γ surface state, where phonon is the sole type of boson in the system. The EPC on Be(0001) Γ surface state was found to be anisotropic by measuring the momentum-dependent mass enhancement factor, λ, which represent the strength of the EPC. Furthermore, the contribution to EPC from each phonon mode (including bulk phonon and surface phonon modes) was revealed by comparing the phonon density of states (DOS) and dispersion relations to the extracted Eliashberg function (ELF), F( k ) 2 , α ω , which represent the EPC detail as function of phonon energy, ω, and electron momentum, k . It is found that the presence of the surface phonon enhances EPC dramatically on Be(0001). However, the most striking result is the observation of the low energy coupling features which might originate from the interaction of electron to the mixing of bulk phonon mode (BPM) and surface phonon mode (SPM). The mixing of the BPM and SPM was not considered in state-of-the-art theoretical calculation, thus could be the reason for the inconsistency to the experimental results. The detail analysis and comparison in this study demonstrates the pathway toward understanding the EBC. High quality ARPES data and detail information of the boson mode are essential for gaining the insight of EBC in complex materials. |
| Location: | 6-2202 Conf Room |
| Author: | areza@lbl.gov |
