Departmental Colloquium

Probing Charge Transport by Terahertz Time-Domain Spectroscopy

Jie Shan
Case Western Reserve University

Time
Wed. March 29, 2006     1:00 PM     Stirling C

Abstract

Light pulses as short as two optical cycles (~ 5 femtoseconds) can now be produced by modelocked lasers. These pulses have dramatically advanced many areas of ultrafast spectroscopy. In this talk I will describe how we may use such pulses to control and measure electric fields on the femtosecond time scale. One important application of these capabilities is the time-domain spectroscopy in the terahertz or far-infrared spectral region. In this approach one produces a controlled electric-field waveform and measures directly in the time domain the changes in this waveform induced by the sample. I will illustrate the application of the technique to obtain quantitative data on the conductivity of materials without the need of contacts (and, when required, with sub-picosecond time resolution) in two examples: (1) charge transport in photoexcited insulators, and (2) charge transport in nanostructures. Within the first topic, emphasis will be placed on understanding polaronic transport in wide gap materials. Within the second one, I will address such basic issues as how the transport behavior of the bulk material is modified in the nanoscale limit, and how quantization and many-body effects influence the response to an electric field of carriers in nanostructures.

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