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Search Results: 1 - 10 of 31057 matches for " Z. Wasilewski "
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Spin depolarization in quantum dots
Sachrajda, A.S.;Gould, C.;Hawrylak, P.;Feng, Y.;Zawadzki, P.;Wasilewski, Z.;
Brazilian Journal of Physics , 1999, DOI: 10.1590/S0103-97331999000400006
Abstract: we have performed single electron spectroscopy experiments on single lateral quantum dots. we demonstrate that the lateral nature of the tunneling as well as the properties of the 2deg leads can be used to extract new information in the 'spin-flip' regime. calculations confirm that one needs to go beyond the hartree-fock approximation and include correlation effects to explain the experimental observations. the results are found to be consistent with the presence of spin depolarization events at the 'spin-flips'.
Fractal Conductance Fluctuations in a Soft Wall Stadium and a Sinai Billiard
A. S. Sachrajda,R. Ketzmerick,C. Gould,Y. Feng,P. J. Kelly,A. Delage,Z. Wasilewski
Physics , 1997, DOI: 10.1103/PhysRevLett.80.1948
Abstract: Conductance fluctuations have been studied in a soft wall stadium and a Sinai billiard defined by electrostatic gates on a high mobility semiconductor heterojunction. These reproducible magnetoconductance fluctuations are found to be fractal confirming recent theoretical predictions of quantum signatures in classically mixed (regular and chaotic) systems. The fractal character of the fluctuations provides direct evidence for a hierarchical phase space structure at the boundary between regular and chaotic motion.
Exciton lifetime in InAs/GaAs quantum dot molecules
C. Bardot,M. Schwab,M. Bayer,S. Fafard,Z. Wasilewski,P. Hawrylak
Physics , 2005, DOI: 10.1103/PhysRevB.72.035314
Abstract: The exciton lifetimes $T_1$ in arrays of InAs/GaAs vertically coupled quantum dot pairs have been measured by time-resolved photoluminescence. A considerable reduction of $T_1$ by up to a factor of $\sim$ 2 has been observed as compared to a quantum dots reference, reflecting the inter-dot coherence. Increase of the molecular coupling strength leads to a systematic decrease of $T_1$ with decreasing barrier width, as for wide barriers a fraction of structures shows reduced coupling while for narrow barriers all molecules appear to be well coupled. The coherent excitons in the molecules gain the oscillator strength of the excitons in the two separate quantum dots halving the exciton lifetime. This superradiance effect contributes to the previously observed increase of the homogeneous exciton linewidth, but is weaker than the reduction of $T_2$. This shows that as compared to the quantum dots reference pure dephasing becomes increasingly important for the molecules.
Single-photon emission from the natural quantum dots in the InAs/GaAs wetting layer
T. Kazimierczuk,A. Golnik,P. Kossacki,J. Gaj,Z. Wasilewski,A. Babinski
Physics , 2011, DOI: 10.1103/PhysRevB.84.115325
Abstract: Time-resolved microphotoluminescence study is presented for quantum dots which are formed in the InAs/GaAs wetting layer. These dots are due to fluctuations of In composition in the wetting layer. They show spectrally sharp luminescence lines with a low spatial density. We identify lines related to neutral exciton and biexciton as well as trions. Exciton emission antibunching (second order correlation value of g^2(0)=0.16) and biexciton-exciton emission cascade prove non-classical emission from the dots and confirm their potential as single photon sources.
Microwave radiation induced magneto-oscillations in the longitudinal and transverse resistance of a two dimensional electron gas
S. A. Studenikin,M. Potemski,P. T. Coleridge,A. Sachrajda,Z. R. Wasilewski
Physics , 2003, DOI: 10.1016/j.ssc.2003.10.008
Abstract: We confirm the existance of magneto-resistance oscillations in a microwave-irradiated two-dimensional electron gas, first reported in a series of papers by Zhudov et al. and Mani et al. In our experiments, on a sample with a more moderate mobility, the microwave induced oscillations are observed not only in the longitudinal - but also in the transverse-resistance (Hall resistance). The phase of the oscillations is such that the decrease (increase) in the longitudinal resistance is accompanied by an increase (decrease) in the absolute value of the Hall resistance. We believe that these new results provide valuable new information to better understand the origin of this interesting phenomenon.
Negative capacitance effect in semiconductor devices
M. Ershov,H. C. Liu,L. Li,M. Buchanan,Z. R. Wasilewski,A. K. Jonscher
Physics , 1998, DOI: 10.1109/16.725254
Abstract: Nontrivial capacitance behavior, including a negative capacitance (NC) effect, observed in a variety of semiconductor devices, is discussed emphasizing the physical mechanism and the theoretical interpretation of experimental data. The correct interpretation of NC can be based on the analysis of the time-domain transient current in response to a small voltage step or impulse, involving a self-consistent treatment of all relevant physical effects (carrier transport, injection, recharging etc.). NC appears in the case of the non-monotonic or positive-valued behavior of the time-derivative of the transient current in response to a small voltage step. The time-domain transient current approach is illustrated by simulation results and experimental studies of quantum well infrared photodetectors (QWIPs). The NC effect in QWIPs has been predicted theoretically and confirmed experimentally. The huge NC phenomenon in QWIPs is due to the non-equilibrium transient injection from the emitter caused by the properties of the injection barrier and the inertia of the QW recharging.
Coulomb and Spin blockade of two few-electrons quantum dots in series in the co-tunneling regime
M. Ciorga,M. Pioro-Ladrière,P. Zawadzki,J. Lapointe,Z. Wasilewski,A. S. Sachrajda
Physics , 2004, DOI: 10.1103/PhysRevB.70.235306
Abstract: We present Coulomb Blockade measurements of two few-electron quantum dots in series which are configured such that the electrochemical potential of one of the two dots is aligned with spin-selective leads. The charge transfer through the system requires co-tunneling through the second dot which is $not$ in resonance with the leads. The observed amplitude modulation of the resulting current is found to reflect spin blockade events occurring through either of the two dots. We also confirm that charge redistribution events occurring in the off-resonance dot are detected indirectly via changes in the electrochemical potential of the aligned dot.
Non-linear magnetotransport phenomena in high-mobility two-dimensional electrons in InGaAs/InP and GaAs/AlGaAs
S. A. Studenikin,G. Granger,A. Kam,A. S. Sachrajda,Z. R. Wasilewski,P. J. Poole
Physics , 2010,
Abstract: This paper reports on the observation and analysis of magnetotransport phenomena in the nonlinear differential resistance $r_{xx}=dV_{xx}/dI$ of high-mobility InGaAs/InP and GaAs/AlGaAs Hall bar samples driven by direct current, $\Idc$. Specifically, it is observed that Shubnikov -de Haas (SdH) oscillations at large filling factors invert their phase at sufficiently large values of $\Idc$. This phase inversion is explained as being due to an electron heating effect. In the quantum Hall effect regime the $r_{xx}$ oscillations transform into diamond-shaped patterns with different slopes corresponding to odd and even filling factors. The diamond-shaped features at odd filling factors can be used as a probe to determine spin energy gaps. A Zero Current Anomaly (ZCA) which manifests itself as a narrow dip in the $r_{xx}(\Idc)$ characteristics at zero current, is also observed. The ZCA effect strongly depends upon temperature, vanishing above 1 K while the transport diamonds persist to higher temperatures. The transport diamonds and ZCA are fully reproduced in a higher mobility GaAs/AlGaAs Hall bar structure confirming that these phenomena reflect intrinsic properties of two-dimensional systems.
Optical readout of charge and spin in a self-assembled quantum dot in a strong magnetic field
M. Korkusinski,P. Hawrylak,A. Babinski,M. Potemski,S. Raymond,Z. Wasilewski
Physics , 2007, DOI: 10.1209/0295-5075/79/47005
Abstract: We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2 quantum Hall singlet phase of the charged exciton. Increasing or decreasing the magnetic field leads to electronic spin-flip transitions and increasing spin polarization. The increasing total spin of electrons appears as a manifold of closely spaced emission lines, while spin flips appear as discontinuities of emission lines. The number of multiplets and discontinuities measures the number of carriers and their spin. We present a complete analysis of the emission spectrum of a single quantum dot with N=4 electrons and a single hole, calculated and measured in magnetic fields up to 23 Tesla.
Challenges for Polish Learners of English from the Implementing of Learning Strategies in the National Curriculum: A Report
Jacek Wasilewski
Humanising Language Teaching , 2010, DOI: 17559715
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