Ultrafast Carrier Dynamics in Topological Insulators

Menon, Shankar G. (2017) Ultrafast Carrier Dynamics in Topological Insulators. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Shankar G. Menon (12MS027)) 12MS027.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

Topological Insulators are class of materials whose surface is conducting and bulk is insulating. Moreover their surface conductivity is protected from back scattering by Time Reversal Symmetry. These properties make it desirable to understand the properties of these exotic materials in detail. In this work, ultrafast carrier dynamics in Topological Insulators are studied using pump probe and Terahertz spectroscopy. In the pump probe spectroscopy part op- tical phonons were found and their characteristic decay time were studied as a function of uence. The resulting behaviour of shorter decay time at higher uences is interpreted to be due to increased interaction between carriers and phonons. Also a Two Temperature modelling of re ectivity was done using electron and phonon temperature. And the theoretical model were used to fit the experimental data, which again conclusively showed increased inter- action between electron and phonon through the increase in electron-phonon coupling constant. In Terahertz Time Domain Spectroscopy, even though the initial motivation was to study the temperature dependence and carrier inter- action of phonon at 1.9THz along with conductivity modelling using Drude and Lorentz model, the noise in the data restricted the domain of study to conductivity modelling. It was also found out that the oscillations in the con- ductivity, which have been present in our data and have been reported before, were not due to phonons present in the sample.

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