Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session T25: QHE: Microwaves and Periodic Modulation |
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Sponsoring Units: FIAP Chair: Michael Zudov, University of Minnesota Room: D135 |
Wednesday, March 17, 2010 2:30PM - 2:42PM |
T25.00001: Hall-field induced resistance oscillations in tilted magnetic fields Michael Zudov, Anthony Hatke, Loren Pfeiffer, Ken West When a large enough dc current is passed through a high-mobility two-dimensional electron system its differential resistivity exhibits oscillations with the applied magnetic field. These oscillations, known as Hall field-induced resistance oscillations, are believed to originate from impurity scattering between Landau levels tilted by Hall field potential. This talk will present the results of our recent experiments studying Hall field-induced resistance oscillations in tilted magnetic fields. The results show that the oscillations are strongly suppressed by in-plane magnetic field. [Preview Abstract] |
Wednesday, March 17, 2010 2:42PM - 2:54PM |
T25.00002: Shubnikov-de Haas oscillations in microwave-irradiated two-dimensional electron systems Anthony Hatke, Hung-Sheng Chiang, Michael Zudov, John Reno We have studied Shubnikov-de Haas Oscillations in a high-mobility two-dimensional electron system irradiated by microwave radiation up to 100 GHz. We have found that the amplitude of Shubnikov oscillations is suppressed by microwaves in the vicinity of certain magnetic fields. These fields depend on the microwave frequency indicating resonant response. This talk will discuss frequency, temperature, and power dependences of the phenomenon and compare observations to earlier studies by other experimental groups. [Preview Abstract] |
Wednesday, March 17, 2010 2:54PM - 3:06PM |
T25.00003: Effects of strong electric field on acoustic phonon resonances in 2D electronic systems in high Landau levels Ivan Dmitriev, Roman Gellman, Maxim Vavilov This talk will present a quantum kinetic description [1] of phonon-assisted electronic transport in crossed electric and magnetic fields in high Landau levels. It will identify quantum magnetooscillations driven by spatial and spectral resonances set by the voltage across the cyclotron diameter, by the cyclotron frequency, and by the frequency of $2k_F$ acoustic phonon which provides backscattering of electron at the Fermi surface, as observed in recent experiment [2]. The phase, magnitude, and temperature dependence of the phonon-induced magnetooscillations are shown to be very sensitive to the applied voltage or direct current. In particular, in the supersonic regime, where the Hall velocity exceeds the sound velocity, the nonlinear conductivity remains finite at zero temperature, while below the supersonic transition the oscillations get exponentially suppressed at low temperature. \\[4pt] [1] I.A. Dmitriev, R. Gellmann, and M.G. Vavilov, in preparation.\\[0pt] [2] W. Zhang, M. A. Zudov, L. N. Pfeiffer, and K. W. West, Phys. Rev. Lett. 101, 246811 (2008). [Preview Abstract] |
Wednesday, March 17, 2010 3:06PM - 3:18PM |
T25.00004: Magneto-oscillations in differential resistivity in intensely irradiated two-dimensional electron systems Hung-Sheng Chiang, Anthony Hatke, Michael Zudov, Maxim Khodas, Maxim Vavilov, Loren Pfeiffer, Ken West We have studied non-linear magnetotransport in very high Landau levels of two-dimensional electron systems subject to intense microwave radiation. We have observed a new class of microwave-induced magneto-oscillations in differential resistivity. In contrast to microwave-induced oscillations reported earlier, the period of these oscillations is governed not only by microwave frequency but also by its intensity. The effect is best observed in the vicinity of the cyclotron resonance and its harmonics at strong enough ac and dc electric fields. Comparison with theoretical calculations offers a unique way to determine the microwave intensity seen by 2D electrons. [Preview Abstract] |
Wednesday, March 17, 2010 3:18PM - 3:30PM |
T25.00005: Effect of Multiphoton Processes on Differential Magneto-resistance of Two-Dimensional Electron Systems Maxim Vavilov, Maxim Khodas, Hung-Sheng Chiang, Anthony Hatke, Michael Zudov, Loren Pfeiffer, Ken West We apply the quantum kinetic equation to calculate the non-linear current through a two-dimensional electron systems subject to intense microwave radiation and placed in a perpendicular magnetic field. We find that the magneto-resistance exhibits an oscillatory behavior as a function of the microwave power near the cyclotron resonance. We demonstrate that these oscillations can be explained in terms of multiphoton scattering processes. Our theoretical results capture all important characteristics of recent experimental studies of the non-linear magnetotransport in high-mobility systems. [Preview Abstract] |
Wednesday, March 17, 2010 3:30PM - 3:42PM |
T25.00006: Effect of electron-electron scattering on magneto-intersubband resistance oscillations of two dimensional electrons in GaAs quantum well Sergey Vitkalov, A.V. Goran, A.A. Bykov, A.I. Toropov The low-temperature ($4.2 |
Wednesday, March 17, 2010 3:42PM - 3:54PM |
T25.00007: Microwave Transmission Measurements in Gated GaAs/AlGaAs Quantum Wells Kristjan Stone, Ivan Knez, Rui-Rui Du, Michael Manfra, Loren Pfeiffer, Ken West Microwave transmission measurements across a 2D electron system have been previously demonstrated in quantum Hall effect and electronic solids regime [1].~We have developed a co-planar waveguide (CPW) system for experiments in microwave-induced resistance oscillations and zero resistance states. Microwaves from a tunable source (2 - 40 GHz) were fed into our system and coupled to a CPW meander line at 300mK to measure cyclotron resonance peaks from a carbon-doped (100) GaAs/Al$_{x}$Ga$_{1-x}$As quantum well 2D hole system.~Our samples are Hall bars with mobility $\mu $= 0.7-1 $\times $10$^{6}$ cm$^{2}$/Vs and carrier density ranging from 2.02 - 2.26$\times $10$^{11}_{ }$cm$^{-2}$. Each sample has been gated with AuPd using a Si$_{3}$N$_{4}$ dielectric.~A differential power measurement $\Delta \mbox{P }=\mbox{ P}_{\mbox{out}} \mbox{-P}_{\mbox{out}}^{\mbox{gate}} $is taken with the signal from the power sensor triggered from a modulated gate to remove the background microwave signal, yielding a cyclotron resonance peak from the transmission signal.~We are able to fit our cyclotron transmission signal using the Drude model and determine the hole mass and the cyclotron scattering time. Experimental data as well as a brief discussion will be presented. The work at Rice was funded by NSF DMR-0706634. [1] L. W. Engel et al, Phys. Rev. Lett. 71, 2638 (1993). [Preview Abstract] |
Wednesday, March 17, 2010 3:54PM - 4:06PM |
T25.00008: Geometric Resonance in Triangular or Honeycomb Lattices Patterned on Very High-Mobility Quantum Wells Yanhua Dai, R.R. Du, L.N. Pfeiffer, K.W. West In our studies of microwave-induced zero-resistance states, we introduce spatial modulation in the 2D electron system by patterning the Hall bar samples with antidot lattices. Our samples are high-mobility GaAs/AlGaAs quantum wells with electron densities (3- 6) x 10$^{11}$/cm$^{2}$ and mobilities $>$ 9 x 10$^{6}$ cm$^{2}$/Vs. The antidot lattices (triangular or honeycomb) which have a lattice constant between 3 and 10 $\mu $m and a dot diameter between 0. 4 and 2 $\mu $m were patterned with e-beam lithography. Our low temperature (300 mK) magnetotransport measurements reveal exceptionally sharp geometric resonances (GR) in R$_{xx}$ up to 8th order in these samples, with the even-peaks commonly stronger than the odd-peaks. The data cannot be explained satisfactorily by the model of localization of pinned orbits. In particular, our data indicate that in the very high-mobility samples, the primary GR peaks are related to the Zener tunneling between electron Landau orbits as their diameter approaches the lattice constant. Ref. Z. Q. Yuan et al, Phys. Rev. B 74, 075313(2006). [Preview Abstract] |
Wednesday, March 17, 2010 4:06PM - 4:18PM |
T25.00009: Microwave absorption of a 2D electron system in spatially varying perpendicular magnetic field B. A. Magill, A. A. Polyanskii, L. W. Engel, M. P. Lilly, J. A. Simmons, J. L. Reno We report on microwave measurements of a two dimensional electron system (2DES) in a spatially varying magnetic field, B$_{z}$, provided by a ferromagnet in proximity to the sample in a homogenous external field, B$_{z0}$. Dy, permalloy, and neodymium iron boron ferromagnets are used in two configurations, rods and plates with holes in them. The radius, r$_{m}$, of the rods or holes ranges from 0.125 mm to 0.5 mm. The microwave transmission of the 2DES exhibits a resonance which decreases in peak frequency as B$_{z0}$ is increased. We observe peak frequencies from $\sim $ 9.5 GHz to150 MHz for external magnetic fields in a range from .02 Telsa to 1.5 Tesla. We will interpret the data in terms of plasma excitations similar to edge magnetoplasmons [1] but confined along the magnetic field inhomogeneity by the large magnetic field gradients there. The interpretation of the data will utilize profiles of the spatially varying magnetic field obtained by magneto optical imaging using iron garnet indicator films with an in-plane magnetization. [Preview Abstract] |
Wednesday, March 17, 2010 4:18PM - 4:30PM |
T25.00010: Nonlinear growth with the microwave intensity in the microwave radiation-induced magnetoresistance oscillations R. G. Mani, C. Gerl, S. Schmult, W. Wegscheider, V. Umansky We compare the characteristics of inverse-magnetic-field- periodic, radiation-induced magnetoresistance oscillations in GaAs/AlGaAs heterostructures prepared by W. Wegscheider et al., and V. Umansky, by fitting the observed lineshape vs. the radiation power, $P$, in the two MBE materials. We find that the radiation-induced oscillatory $\Delta R_{xx}$, in both materials, can be described by $\Delta R_{xx} = -A exp(-\lambda/B)sin(2 \pi F/B)$, where $A$ is the amplitude, $\lambda$ is the damping parameter, and $F$ is the oscillation frequency. Both $\lambda$ and $F$ turn out to be insensitive to $P$. On the other hand, $A$ grows nonlinearly with $P$. [Preview Abstract] |
Wednesday, March 17, 2010 4:30PM - 4:42PM |
T25.00011: Microwave polarization study of radiation-induced magneto-resistance oscillations Tarek Ghanem, R. G. Mani, W. Wegscheider Under microwave irradiation, high mobility GaAs/AlGaAs samples display radiation-induced magnetoresistance oscillations and zero resistance states. These novel phenomena have attracted significant theoretical and experimental efforts over the last few years. Here, we experimentally investigate the effect of polarization direction for linearly polarized microwaves on the radiation induced magnetoresistance oscillations. Previous investigations suggest the independence of the oscillations on the polarization direction in consistency with theoretical predictions (Jes\'{u}s I\~{n}arrea and Gloria Platero, PRB 76, 073311~(2007)). Here, we present the results of our study and discuss the implications of the results for existing theoretical models. [Preview Abstract] |
Wednesday, March 17, 2010 4:42PM - 4:54PM |
T25.00012: The Terahertz Frequency Hall Conductivity of a High-Mobility Two-Dimensional Electron Gas Jeremy Curtis, Jon Moore, Takahisa T. Tokumoto, Judy Cherian, Junichiro Kono, Alexey Belyanin, Stephen McGill, David Hilton We have performed the first measurement of the \emph{terahertz-frequency} complex conductivity tensor of a Landau-quantized high mobility ($10^{6}$ cm$^{2}$ V$^{-1}$ s$^{-1}$) GaAs two-dimensional electron gas. We use polarization-sensitive ultrafast terahertz magnetospectroscopy to resolve the on-axis and off-diagonal Hall conductivity elements. We focus our measurements near cyclotron resonance to determine the line width from 0.4 K to 100 K at $\pm$1.25 T. This line width decreases monotonically with temperature and does not saturate at the lowest temperatures measured. In this talk, we will develop a model of these data to discuss the relative influence of electron-electron, electron-phonon, and impurity scattering on the temperature dependent sample mobility. [Preview Abstract] |
Wednesday, March 17, 2010 4:54PM - 5:06PM |
T25.00013: Anomalous saturation of the temperature dependent resistivity in the deep insulating regime of 2D electron layers in high-quality mesoscopic GaAs/AlGaAs structures David Neilson, Alex Hamilton We analyze properties of mesoscopic low density GaAs 2D electron systems with short-ranged disorder. We show that inhomogeneities can cause the resistivity to saturate as $T\rightarrow 0$, instead of increasing exponentially as happens in macroscopic samples. This effect is associated with the break up of the 2D system into metallic and insulating domains. In mesoscopic systems in the insulating phase, the isolated metallic domains can be very closely spaced. At low temperature, the close proximity favors direct tunneling between states at the chemical potential on adjacent metallic domains instead of conventional variable-range hopping. Our calculated temperature-dependent transmission rates reproduce all the features of recent measurements of the resistivity $\rho(T)$ in 2D electron layers in gated mesoscopic GaAs/AlGaAs structures [Baenninger {\it et al.}, Phys.\ Rev.\ Lett.\ {\bf 100}, 016805 (2008)]. In particular, even when $\rho>>h/e^2$, the insulating exponential increase in $\rho(T)$ can saturate or show a metallic-like drop as the temperature goes to zero. [Preview Abstract] |
Wednesday, March 17, 2010 5:06PM - 5:18PM |
T25.00014: High bandwidth measurements of large area 2-Dimensional systems using rf reflectometry L.J. Taskinen, R.P. Starrett, T.P. Martin, A.P. Micolich, A.R. Hamilton, M.Y. Simmons, D.A. Ritchie, M. Pepper We have embedded AlGaAs/GaAs based 2 dimensional electron and hole systems in a large area Hall bar into an impedance matching LC circuit terminating a transmission line, and used rf reflectometry to measure temporal changes in the resistance of the device at mK temperatures. We have shown that, contrary to initial estimations, it is feasible to use this method with large 2D devices despite the large capacitance, increasing the measurement bandwidth up to tens of megahertz [1]. As an example, we have mapped the Landau level evolution in a 2DHS as a function of magnetic field and gate voltage much faster than would be possible using standard lock-in technique [1].\\[4pt] [1] L. J. Taskinen et al., Rev. Sci. Inst. {\bf 79}, 123901, (2008). [Preview Abstract] |
Wednesday, March 17, 2010 5:18PM - 5:30PM |
T25.00015: In-plane magnetoresistivity of high-mobility two-dimensional electrons in an undoped Si/SiGe quantum well at 20 mK T. M. Lu, W. Pan, D. C. Tsui, C.-H. Lee, C. W. Liu Two-dimensional electron gas (2DEG) in a Si quantum well with mobility over 1$\times $10$^{6}$ cm$^{2}$/Vs has been realized using an undoped Si/SiGe heterostructure. In this high quality 2DEG, the 2D metal-insulator transition occurs at a characteristic density n$_{c}$=1.35$\times $10$^{10}$/cm$^{2}$, the lowest reported in the Si systems. We have further measured the in-plane magnetoresistivity at 20mK. It is observed that, in sharp contrast to modulation-doped heterostructures with lower electron mobility where the ratio of the saturation resistance in high in-plane magnetic field to the zero-magnetic-field resistance is strongly enhanced near n$_{c}$, no such enhancement is observed in this high-mobility undoped field-effect transistor. The characteristic magnetic field, B$_{S}$, at which the in-plane magnetoresistivity saturates, follows the linear electron density dependence previously observed in modulation-doped structures at high densities. However, B$_{S}$ deviates considerably from this linear dependence at low densities and does not extrapolates to a finite density at B$_{S}$ =0. [Preview Abstract] |
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