Fano Signatures in the Intersubband Terahertz Response of Optically Excited Semiconductor Quantum Wells
FZD News - 30/03/09 - Link zur Pressemitteilung der Philipps-Universität Marburg
Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.
(a) Optical interband pump intersubband THz probe experiment.
(b) The transition from the heavy-hole (hh) state to the first conduction state (c1) in the Al0:34Ga0:66As=GaAs multiquantum- well (MQW) sample is resonantly excited, either by a ps or a fs laser. THz pulses probe the c1-to-c2 transition 25 ps after photoexcitation.
(c) The field transients of the transmitted THz pulses are detected by phase-matched electro-optic sampling with a sampling beam. The reference without photoexcitation is shown.
In summary, it could be shown how the emission by the ponderomotive motion of the excited carriers can directly be identified in the linear THz response. Using a microscopic theory for the THz response, the observed Fano-like features in the transmission spectrum can unambiguously be attributed to the phase sensitive superposition of the intersubband resonance and the ponderomotive carrier dynamics. These results are connected to the typical Fano situation because the system has a sharp discrete intersubband resonance that interferes with a broad continuous contribution, i.e., the ponderomotive current density. However, one of the contributions in this case is nonabsorptive such that one could not observe the Fano resonance in the absorption spectrum but in the differential transmission spectrum only.
D. Golde,1,* M. Wagner,2 D. Stehr,2 H. Schneider,2 M. Helm,2 A. M. Andrews,3 T. Roch,3 G. Strasser,3 M. Kira,1 and S.W. Koch1: "Fano Signatures in the Intersubband Terahertz Response of Optically Excited Semiconductor Quantum Wells", in: PhysRevLett.102.127403, DOI: 10.1103.
1 Department of Physics and Materials Sciences Center, Philipps-University, Renthof 5, 35032 Marburg, Germany
2 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany
3 Solid State Electronics Institute, Micro- & Nanostructure Center, TU Wien
Prof. Manfred Helm
Institute of Ion Beam Physics and Materials Research
Phone: ++49 351 260 2260