TY - JOUR T1 - Undressing a collective intersubband excitation in a quantum well JF - Physical Review Letters Y1 - 1996 A1 - Craig, K. A1 - Galdrikian, B. A1 - Heyman, J. N. A1 - Markelz, A. G. A1 - Williams, J. B. A1 - Sherwin, M. S. A1 - Campman, K. A1 - Hopkins, P. F. A1 - Gossard, A. C. AB -

We have experimentally measured the 1-2 intersubband absorption in a single 40 nm wide modulation-doped Al0.3Ga0.7As/GaAs square quantum well as a function of frequency, intensity, and charge density. The low-intensity depolarization-shifted absorption occurs near 80 cm(-1) (10 meV or 2.4 THz), nearly 30% higher than the intersubband spacing. At higher intensities, the absorption peak shifts to lower frequencies. Our data are in good agreement with a theory proposed by Zaluzny, which attributes the redshift to a reduction in the depolarization shift as the excited subband becomes populated.

VL - 76 SN - 0031-9007 N1 - Sherwin, Mark S/Q-4762-2017
Sherwin, Mark S/0000-0002-3869-1893; Markelz, Andrea/0000-0003-0443-4319
78 ER - TY - JOUR T1 - NONLINEAR QUANTUM DYNAMICS IN SEMICONDUCTOR QUANTUM-WELLS JF - Physica D-Nonlinear Phenomena Y1 - 1995 A1 - Sherwin, M. S. A1 - Craig, K. A1 - Galdrikian, B. A1 - Heyman, J. A1 - Markelz, A. A1 - Campman, K. A1 - Fafard, S. A1 - Hopkins, P. F. A1 - Gossard, A. AB -

We discuss recent measurements of the nonlinear response of electrons in wide quantum wells driven by intense electromagnetic radiation at terahertz frequencies. The theme is the interplay of quantum mechanics, strong periodic driving, the electron-electron interaction and dissipation. We discuss harmonic generation from an asymmetric double quantum well in which the effects of dynamic screening are important. Measurements and theory are found to be in good agreement. We also discuss intensity-dependent absorption in a 400 Angstrom square quantum well. A new nonlinear quantum effect occurs, in which the frequency at which electromagnetic radiation is absorbed shifts to the red with increasing intensity. The preliminary experimental results are in agreement with a theory by Zaluzny, in which the source of the nonlinearity is the self-consistent potential in the Hartree approximation for the electron dynamics.

VL - 83 SN - 0167-2789 N1 - Sherwin, Mark S/Q-4762-2017
Sherwin, Mark S/0000-0002-3869-1893; Markelz, Andrea/0000-0003-0443-4319
14th Annual International Conference of the Center-for-Nonlinear-Studies - Quantum Complexity in Mesoscopic Systems
May 16-20, 1994
Los alamos, nm
Ctr nonlinear studies
34 ER - TY - JOUR T1 - RESONANT-ENERGY RELAXATION OF TERAHERTZ-DRIVEN 2-DIMENSIONAL ELECTRON GASES JF - Physical Review B Y1 - 1995 A1 - Asmar, N. G. A1 - Markelz, A. G. A1 - Gwinn, E. G. A1 - Cerne, J. A1 - Sherwin, M. S. A1 - Campman, K. L. A1 - Hopkins, P. F. A1 - Gossard, A. C. VL - 51 SN - 0163-1829 N1 - Sherwin, Mark S/Q-4762-2017
Sherwin, Mark S/0000-0002-3869-1893; Markelz, Andrea/0000-0003-0443-4319
119 ER - TY - JOUR T1 - DC TRANSPORT IN INTENSE, INPLANE TERAHERTZ ELECTRIC-FIELDS IN AL(X)GA(1-X)AS HETEROSTRUCTURES AT 300-K JF - Solid-State Electronics Y1 - 1994 A1 - Asmar, N. G. A1 - Markelz, A. G. A1 - Gwinn, E. G. A1 - Hopkins, P. F. A1 - Gossard, A. C. AB -

We report 300 K studies of the dependence of the in-plane, d.c. conductivity, sigma(d.c.) (E(omega)), of a quasi 2D electron gas on the amplitude E(omega) and frequency of intense, far-infrared fields (omega/2pi = 0.24-3.5 THz). We measure sigma(d.c.) (E(omega) parallel-to E(d.c.)), where E(d.c.) is a small sensing field, and observe a monotonic decrease in sigma(d.c.) with increasing E(omega). Although a simple scaling ansatz collapses the measured sigma(d.c.) (E(omega)) data onto a single curve for frequencies from 0.25-3.45 THz (at low to moderate scaled fields), the decrease in conductivity is substantially more rapid than expected from comparison to similar data taken by Masselink et al. [Solid-St. Electron. 31, 337 (1988)] at 35 GHz. We tentatively attribute this difference to effects of a high-frequency modulation in the electron temperature.

VL - 37 SN - 0038-1101 N1 - Markelz, Andrea/0000-0003-0443-4319
6th International Conference on Modulated Semiconductor Structures
Aug 23-27, 1993
Garmisch partenkir, germany
Tech univ munchen, walter schottky inst
1 ER - TY - JOUR T1 - ENERGY RELAXATION AT THZ FREQUENCIES IN ALXGA1-XAS HETEROSTRUCTURES JF - Semiconductor Science and Technology Y1 - 1994 A1 - Asmar, N. G. A1 - Markelz, A. G. A1 - Gwinn, E. G. A1 - Hopkins, P. F. A1 - Gossard, A. C. AB -

We report 4.2 K studies of the dependence of the in-plane, DC conductivity of a quasi 2D electron gas on the amplitude E(omega) of applied fields with frequencies from 0.25 THz to 3.5 THz. We analyse the dependence of sigma(DC) on E(omega) assuming that electron-optical phonon scattering dominates energy relaxation, that the absorbed power has a Drude form and that the electron distribution is thermal. This simple analysis is self-consistent: Arrhenius plots of the estimated energy loss rate have a slope near -homega(LO)BAR/k(B) for all frequencies, as expected for energy loss by optical phonon emission. We find that the effective energy relaxation time tau(epsilon) varies with the frequency of the applied field, from tau(epsilon) approximately 4 ps at 0.34 THz to tau(epsilon) approximately 0.3 ps at 3.45 THz. This may indicate a frequency-dependent form for the hot-phonon distribution.

VL - 9 SN - 0268-1242 N1 - Markelz, Andrea/0000-0003-0443-4319
S
8th International Conference on Hot Carriers in Semiconductors
Aug 16-20, 1993
Oxford univ, oxford, england
Sci & engn res council; royal soc; brit council; oxford univ
2 JO - Semicond. Sci. Technol. ER - TY - JOUR T1 - FAR-INFRARED SATURATION SPECTROSCOPY OF A SINGLE SQUARE-WELL JF - Semiconductor Science and Technology Y1 - 1994 A1 - Craig, K. A1 - Felix, C. L. A1 - Heyman, J. N. A1 - Markelz, A. G. A1 - Sherwin, M. S. A1 - Campman, K. L. A1 - Hopkins, P. F. A1 - Gossard, A. C. AB -

We have performed saturation spectroscopy measurements of the lowest intersubband transition in a single 400 angstrom GaAs/Al0.3Ga0.7As modulation-doped square quantum well. We couple intense tunable far-infrared radiation from the Santa Barbara free electron laser into our sample using an edge-coupling technique and measure absorption as a function of frequency and intensity. Saturation and frequency shifts in the absorption line are clearly observed. We attribute the frequency shifts to reductions in the many-body depolarization shift. From our preliminary measurements, we estimate the intersubband relaxation time to be 600 ps to within a factor of three.

VL - 9 SN - 0268-1242 N1 - Sherwin, Mark S/Q-4762-2017
Sherwin, Mark S/0000-0002-3869-1893; Markelz, Andrea/0000-0003-0443-4319
S
8th International Conference on Hot Carriers in Semiconductors
Aug 16-20, 1993
Oxford univ, oxford, england
Sci & engn res council; royal soc; brit council; oxford univ
31 JO - Semicond. Sci. Technol. ER - TY - JOUR T1 - PROBING TERAHERTZ DYNAMICS IN SEMICONDUCTOR NANOSTRUCTURES WITH UCSB FREE-ELECTRON LASERS JF - Journal of Luminescence Y1 - 1994 A1 - Allen, S. J. A1 - Craig, K. A1 - Felix, C. L. A1 - Guimaraes, P. A1 - Heyman, J. N. A1 - Kaminski, J. P. A1 - Keay, B. J. A1 - Markelz, A. G. A1 - Ramian, G. A1 - Scott, J. S. A1 - Sherwin, M. S. A1 - Campman, K. L. A1 - Hopkins, P. F. A1 - Gossard, A. C. A1 - Chow, D. A1 - Lui, M. A1 - Liu, T. Y. AB -

The UCSB free-electron lasers provide kilowatts of continuously tunable radiation from 120 GHz to 4.8 THz. They have the most impact on terahertz science and technology that require a tunable, high power source to explore non-linear dynamics or that sacrifice incident power to recover the linear response of systems with very small cross-section. We describe three experiments that demonstrate the utility of these lasers in experiments on the terahertz dynamics of semiconductor nanostructures: (i) terahertz dynamics of resonant tunneling diodes, (ii) saturation spectroscopy of quantum wells and (iii) photon-assisted tunneling in superlattices.

VL - 60-1 SN - 0022-2313 N1 - Sherwin, Mark S/Q-4762-2017; Guimaraes, Paulo Sergio Soares/B-6918-2012
Sherwin, Mark S/0000-0002-3869-1893; Guimaraes, Paulo Sergio Soares/0000-0002-0113-2641; Markelz, Andrea/0000-0003-0443-4319
1993 International Conference on Luminescence (ICL 93)
Aug 09-13, 1993
Univ connecticut, storrs, ct
Univ connecticut; opt soc amer; amer phys soc; ieee, laser & electro opt soc; int union pure & appl phys; int sci fdn; univ connecticut res fdn
3 ER - TY - Generic T1 - Far-infrared nonlinear response of electrons in semiconductor nanostructures T2 - SPIE Proceedings Y1 - 1993 A1 - Sherwin, M. S. A1 - Asmar, N. G. A1 - Bewley, W. W. A1 - Craig, K. A1 - Felix, C. L. A1 - Galdrikian, B. A1 - Gwinn, E. G. A1 - Markelz, A.G. A1 - Gossard, A. C. A1 - Hopkins, P. F. A1 - Sundaram, M. A1 - Birnir, B. JF - SPIE Proceedings VL - 1854 ER -