Dynamics of photo-excited bismuth
Abstract/Contents
- Abstract
- The dynamics of photo-excited semi-metallic bismuth are determined by the strong interactions between the electronic and lattice degrees of freedom. In this thesis, I present results from ultrafast optical and x-ray experiments that explore the nonequilibrium behavior of photo-excited bismuth and help elucidate the coupling between these degrees of freedom. First of all, there has been sustained interest in the coupling between the photo-excited carriers and the zone-center longitudinal (A1g) optical phonon, as it relates directly to the magnitude of the Peierls distortion. Therefore, I have used optical pump-probe method to study the inverse Peierls distortion by directly looking at the A1g phonons under high carrier photo-excitation. In addition, the mechanism of ultrafast-excitation of A1g and Eg (transverse optical) phonon modes has been widely studied but not yet fully understood. Older models, including Impulsive Stimulated Raman Scattering (ISRS) the Displacive Excitation of Coherent Phonons (DECP) cannot perfectly explain the discrepancy of the data between spontaneous and time-resolved Raman scattering. We show that elements of both models are responsible for the excitation mechanism and attribute the weak coupling to the coherent Eg mode as due to the fragile Eg electronic coherence, and in the process of figuring out a novel way of probing extremely fast electron decoherence rates. Optical experiments are primarily sensitive to zone-center excitations. To further understand the non-zero momentum phonon behavior of photo-excited Bi as well as the ultrafast melting process, I have utilized time resolved x-ray diffuse scattering using different X-ray sources, including synchrotron generation and X-ray free electron lasers (FEL). I have observed thermally activated phonons whose lifetime is consistent with the thermal transport characteristic time. This time scale also dictates the epitaxial regrowth following laser induced melting. Non-equillibrium phonons, which live for hundreds of ps have also been observed, similar to our earlier observation in polar semiconductors. With better time resolution (~100 fs) from the Linac Coherent Light Source (LCLS), we were able to produce and observe large momentum squeezed phonons. Experimental results were consistent with simulation from first principle calculations throughout the Brillouin Zone (BZ). Ultrafast melting measurements with 100 fs resolution show results consistent with observations from earlier ultrafast electron diffraction. Moreover, they also show for the first time the highly anisotropic phonon softening, which lives for up to 1 ps, before the melting happens.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2013 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Chen, Jian |
|---|---|
| Associated with | Stanford University, Department of Applied Physics. |
| Primary advisor | Reis, David A, 1970- |
| Thesis advisor | Reis, David A, 1970- |
| Thesis advisor | Bucksbaum, Philip H |
| Thesis advisor | Fisher, Ian R. (Ian Randal) |
| Advisor | Bucksbaum, Philip H |
| Advisor | Fisher, Ian R. (Ian Randal) |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Jian Chen. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2013. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2013 by Jian Chen
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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