01295nas a2200241 4500008004100000020001400041245007000055210006900125260001100194300001400205490000700219520060900226100001400835700001900849700001900868700002000887700002100907700002000928700001600948700002000964700002000984856004901004 1996 eng d a0031-900700aUndressing a collective intersubband excitation in a quantum well0 aUndressing a collective intersubband excitation in a quantum wel cMar 25 a2382-23850 v763 a
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.
1 aCraig, K.1 aGaldrikian, B.1 aHeyman, J., N.1 aMarkelz, A., G.1 aWilliams, J., B.1 aSherwin, M., S.1 aCampman, K.1 aHopkins, P., F.1 aGossard, A., C. uhttps://markelz.physics.buffalo.edu/node/26501583nas a2200241 4500008004100000020001400041245006200055210006100117260001100178300001200189490000700201520093300208100002001141700001401161700001901175700001501194700001601209700001601225700001501241700002001256700001601276856004901292 1995 eng d a0167-278900aNONLINEAR QUANTUM DYNAMICS IN SEMICONDUCTOR QUANTUM-WELLS0 aNONLINEAR QUANTUM DYNAMICS IN SEMICONDUCTOR QUANTUMWELLS cMay 15 a229-2420 v833 aWe 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.
1 aSherwin, M., S.1 aCraig, K.1 aGaldrikian, B.1 aHeyman, J.1 aMarkelz, A.1 aCampman, K.1 aFafard, S.1 aHopkins, P., F.1 aGossard, A. uhttps://markelz.physics.buffalo.edu/node/27200655nas a2200217 4500008004100000020001400041245008000055210006900135260001100204300001600215490000700231100001800238700002000256700001800276700001400294700002000308700002000328700002000348700002000368856004900388 1995 eng d a0163-182900aRESONANT-ENERGY RELAXATION OF TERAHERTZ-DRIVEN 2-DIMENSIONAL ELECTRON GASES0 aRESONANTENERGY RELAXATION OF TERAHERTZDRIVEN 2DIMENSIONAL ELECTR cJun 15 a18041-180440 v511 aAsmar, N., G.1 aMarkelz, A., G.1 aGwinn, E., G.1 aCerne, J.1 aSherwin, M., S.1 aCampman, K., L.1 aHopkins, P., F.1 aGossard, A., C. uhttps://markelz.physics.buffalo.edu/node/25901474nas a2200193 4500008004100000020001400041245010700055210006900162260001200231300001200243490000700255520087300262100001801135700002001153700001801173700002001191700002001211856004901231 1994 eng d a0038-110100aDC TRANSPORT IN INTENSE, INPLANE TERAHERTZ ELECTRIC-FIELDS IN AL(X)GA(1-X)AS HETEROSTRUCTURES AT 300-K0 aDC TRANSPORT IN INTENSE INPLANE TERAHERTZ ELECTRICFIELDS IN ALXG cApr-Jun a693-6950 v373 aWe 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.
1 aAsmar, N., G.1 aMarkelz, A., G.1 aGwinn, E., G.1 aHopkins, P., F.1 aGossard, A., C. uhttps://markelz.physics.buffalo.edu/node/26001472nas a2200193 4500008004100000020001400041245007200055210006900127260000800196300001200204490000600216520091100222100001801133700002001151700001801171700002001189700002001209856004901229 1994 eng d a0268-124200aENERGY RELAXATION AT THZ FREQUENCIES IN ALXGA1-XAS HETEROSTRUCTURES0 aENERGY RELAXATION AT THZ FREQUENCIES IN ALXGA1XAS HETEROSTRUCTUR cMay a828-8300 v93 aWe 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.
1 aAsmar, N., G.1 aMarkelz, A., G.1 aGwinn, E., G.1 aHopkins, P., F.1 aGossard, A., C. uhttps://markelz.physics.buffalo.edu/node/26101316nas a2200229 4500008004100000020001400041245006500055210006300120260000800183300001200191490000600203520067700209100001400886700001800900700001900918700002000937700002000957700002000977700002000997700002001017856004901037 1994 eng d a0268-124200aFAR-INFRARED SATURATION SPECTROSCOPY OF A SINGLE SQUARE-WELL0 aFARINFRARED SATURATION SPECTROSCOPY OF A SINGLE SQUAREWELL cMay a627-6290 v93 aWe 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.
1 aCraig, K.1 aFelix, C., L.1 aHeyman, J., N.1 aMarkelz, A., G.1 aSherwin, M., S.1 aCampman, K., L.1 aHopkins, P., F.1 aGossard, A., C. uhttps://markelz.physics.buffalo.edu/node/26401594nas a2200337 4500008004100000020001400041245009400055210006900149260000800218300001200226490000900238520066100247100001800908700001400926700001800940700001800958700001900976700002100995700001701016700002001033700001501053700001801068700002001086700002001106700002001126700002001146700001301166700001201179700001601191856004901207 1994 eng d a0022-231300aPROBING TERAHERTZ DYNAMICS IN SEMICONDUCTOR NANOSTRUCTURES WITH UCSB FREE-ELECTRON LASERS0 aPROBING TERAHERTZ DYNAMICS IN SEMICONDUCTOR NANOSTRUCTURES WITH cApr a250-2550 v60-13 aThe 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.
1 aAllen, S., J.1 aCraig, K.1 aFelix, C., L.1 aGuimaraes, P.1 aHeyman, J., N.1 aKaminski, J., P.1 aKeay, B., J.1 aMarkelz, A., G.1 aRamian, G.1 aScott, J., S.1 aSherwin, M., S.1 aCampman, K., L.1 aHopkins, P., F.1 aGossard, A., C.1 aChow, D.1 aLui, M.1 aLiu, T., Y. uhttps://markelz.physics.buffalo.edu/node/25700717nas a2200241 4500008004100000245008100041210006900122300001000191490000900201100002000210700001800230700001900248700001400267700001800281700001900299700001800318700001800336700002000354700002000374700001700394700001500411856004900426 1993 eng d00aFar-infrared nonlinear response of electrons in semiconductor nanostructures0 aFarinfrared nonlinear response of electrons in semiconductor nan a36-470 v18541 aSherwin, M., S.1 aAsmar, N., G.1 aBewley, W., W.1 aCraig, K.1 aFelix, C., L.1 aGaldrikian, B.1 aGwinn, E., G.1 aMarkelz, A.G.1 aGossard, A., C.1 aHopkins, P., F.1 aSundaram, M.1 aBirnir, B. uhttps://markelz.physics.buffalo.edu/node/320