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WFU Physics Seminars

WFU Physics Colloquium

TITLE: "Pulsed Terahertz Spectroscopy of Collective Modes in Perovskites and Biomoleculdes"

SPEAKER: Dr. Andrea Markelz,

University of Maryland and Lucent Technologies

TIME: 4 PM, Wednesday, April 21, 1999

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Refreshments will be served at 3:30 PM in the lounge. All interested persons are cordially invited to attend.

ABSTRACT

Spectroscopy in the terahertz (THz) frequency range is important for a variety of material systems. THz conductivity measurements probe the frequency dependent charged carrier scattering at frequencies on the order of the average relaxation rate for semiconductors. In addition collective excitations in both solid state and molecular systems lie in this frequency range. Besides revealing the underlying physics, these measurements are relevant to developing communications technology where industry is striving to develop optical switching speeds at THz frequencies. In the past the THz range has been difficult to access. The development of pulsed THz spectroscopy (PTS) suggests that this method is ideal both as a materials charaterization tool and as a method to study the time evolution of low frequency dynamics under electronic or photonic perturbation. We will discuss measurements using PTS to study the novel properties in several perovskite systems: ferroelectrics, colossal magnetoresistance materials, and high temperature superconductors. We then turn to a somewhat different condensed matter system, that of biomolecules. Here the movements associated with low frequency vibrational modes are the same collective motions necessary to achieve a conformational change. Such conformational changes are critical to bioactivity. We discuss initial measurements of these conformational vibrational modes using PTS and then how this novel spectroscopic tool can be used actually follow energy dissipation in both biomolecular and solid state systems.

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