Europhys. Lett.
Volume 70, Number 4, May 2005
Page(s) 534 - 540
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 15 April 2005
Europhys. Lett., 70 (4), pp. 534-540 (2005)
DOI: 10.1209/epl/i2005-10014-6

THz collective oscillations of ballistic electrons in wide potential wells: Bridging classical transport with quantum dynamics

M. Eckardt1, M. Betz2, A. Schwanhäußer1, S. Trumm2, F. Sotier2, 3, L. Robledo1, S. Malzer1, 4, T. Müller5, K. Unterrainer5, A. Leitenstorfer2, 3 and G. H. Döhler1, 4

1  Lehrstuhl für Halbleiterphysik, Universität Erlangen - D-91054 Erlangen, Germany
2  Physik-Department E 11, Technische Universität München D-85748 Garching, Germany
3  Fachbereich Physik, Universität Konstanz - D-78457 Konstanz, Germany
4  Max-Planck-Forschungsgruppe für Optik, Information und Photonik Universität Erlangen-Nürnberg - D-91058 Erlangen, Germany
5  Institut für Festkörperelektronik, Technische Universität Wien - Wien, Austria

received 20 January 2005; accepted in final form 29 March 2005
published online 15 April 2005

Parabolic shaped potential wells of a width between 120$\un{nm}$ and 250$\un{nm}$ are defined in a band gap engineered $\ab{p}^{+}$-n- $\ab{p}^{+}$ heterostructure. After femtosecond photoinjection of carriers near the boundary of the well, electrons are found to coherently oscillate across the well with the classical harmonic-oscillator frequency of a few THz instead of performing the intuitively expected unidirectional relaxation towards the bottom of the well. Most strikingly, the coherence of this periodic electron motion is maintained despite multiple phonon scattering events. This novel transport regime is predicted by detailed Monte Carlo simulations and verified by analyzing the femtosecond transmission of the heterostructure as well as by directly detecting the THz radiation emitted by the oscillating electron-hole dipole. By decreasing the well width, this semi-classical ballistic transport regime is expected to converge towards a quantum-beat regime.

78.47.+p - Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter.
73.23.Ad - Ballistic transport.
73.63.Hs - Quantum wells.

© EDP Sciences 2005