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HL: Fachverband Halbleiterphysik

HL 29: Symposium THZ interactions

HL 29.2: Invited Talk

Wednesday, March 28, 2007, 14:45–15:15, H15

Ultrafast THz Spectroscopy of Carrier Correlations in Complex Materials — •Robert A. Kaindl — Department of Physics, UC Berkeley and Materials Sciences Division, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

Coulomb interactions in a many-body system can lead to correlated states with fundamentally new physical properties. I will discuss experiments that employ coherent THz pulses and direct field-resolved detection to probe time-varying correlations of photoexcited electron-hole pairs and Cooper pair condensates. The THz electromagnetic response of short-lived exciton states in bulk and nanoscale semiconductors shows characteristic inter-level transitions in analogy to atoms. Intra-excitonic spectroscopy provides new tools to measure and control exciton gases. I will review experiments that trace the temperature, density, excitation energy, and time dependence of intra-excitonic resonances, to directly map out excitonic phase diagrams and to follow exciton formation and ionization kinetics. Moreover, in single-walled carbon nanotubes, THz pulses enable a contact-less detection of charge conductivity. In high-Tc superconductors, the THz-frequency electromagnetic response couples directly to Cooper pair condensates and to quasiparticle excitations. We observe transient changes in the THz conductivity of Bi-2212 that occur after ultrafast depletion of the superconducting condensate. The temporal decay reveals a bimolecular kinetics of charge pair formation. Work performed in collaboration with M. A. Carnahan, D. Hägele, R. Huber, B. A. Schmid, Y. Ma, G. Fleming, S. Oh, J. Eckstein, and D. S. Chemla.