Download or read book Spin Dynamics in High mobility Two dimensional Electron Systems Embedded in GaAs AlGaAs Quantum Wells written by Michael Griesbeck and published by . This book was released on 2012 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Non diffusive Spin Dynamics in a Two dimensional Electron Gas written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs/GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wavevector range from zero to 6 x 104 cm−1. We find that the spin polarization lifetime is maximal at nonzero wavevector, in contrast with expectation based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling.
Download or read book Non diffusive Spin Dynamics in a Two dimensional Electrongas written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We describe measurements of spin dynamics in thetwo-dimensional electron gas in GaAs/GaAlAs quantum wells. Opticaltechniques, including transient spin-grating spectroscopy, are used toprobe the relaxation rates of spin polarization waves in the wavevectorrange from zero to 6E4 cm-1. We find that the spin polarization lifetimeis maximal at nonzero wavevector, in contrast with expectation based onordinary spin diffusion, but in quantitative agreement with recenttheories that treat diffusion in the presence of spin-orbitcoupling.
Download or read book Spin Dynamics in Two Dimensional Quantum Materials written by Marc Vila Tusell and published by Springer Nature. This book was released on 2021-11-10 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on the exploration of nontrivial spin dynamics in graphene-based devices and topological materials, using realistic theoretical models and state-of-the-art quantum transport methodologies. The main outcomes of this work are: (i) the analysis of the crossover from diffusive to ballistic spin transport regimes in ultraclean graphene nonlocal devices, and (ii) investigation of spin transport and spin dynamics phenomena (such as the (quantum) spin Hall effect) in novel topological materials, such as monolayer Weyl semimetals WeTe2 and MoTe2. Indeed, the ballistic spin transport results are key for further interpretation of ultraclean spintronic devices, and will enable extracting precise values of spin diffusion lengths in diffusive transport and guide experiments in the (quasi)ballistic regime. Furthermore, the thesis provides an in-depth theoretical interpretation of puzzling huge measured efficiencies of the spin Hall effect in MoTe2, as well as a prediction of a novel canted quantum spin Hall effect in WTe2 with spins pointing in the yz plane.
Download or read book Time resolved Studies of Electron and Hole Spin Dynamics in Modulation doped GaAs AlGaAs Quantum Wells Elektronisk Resurs written by Tobias Korn and published by . This book was released on 2010 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spin dynamics in semiconductors have gained much interest in the past years due to the emerging field of semiconductor spintronics. This review is focussed on the observation and control of electron and hole spin dynamics in modulation-doped heterostructures based on the GaAs/AlGaAs material system. Modulation doping allows for the creation of two-dimensional electron and hole systems with high carrier mobility. By confining carriers to a two-dimensional sheet, the spin-orbit interaction is modified significantly. In addition to this, it can be further modified by changing the symmetry of the system, for example by externally applied or built-in electric fields along the growth direction. Our recent experimental results on spin dynamics in two dimensions are reviewed and discussed in connection with theoretical considerations. A brief overview of the current research challenges in this field is given.
Download or read book Electrical Control of the Electron Spin Dynamics in 111 oriented GaAs AGaAs Quantum Wells written by Quang ha Duong and published by . This book was released on 2013 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have studied the electron spin dynamics in 111-oriented GaAs/AlGaAs quantum wells grown on 111-substrate by time-resolved photoluminescence spectroscopy. By applying an external electric field about 50 kV/cm along growth direction, we observed the spectacular increase of electron spin which can attain values greater than 30 ns. This phenomenon comes from the electrical control of spin-orbit interaction in conduction band that make the Rashba term compensate exactly with the Dresselhaus term. The cancellation effect of these two terms results in the suppression of electron spin relaxation induced by D'yakonov-Perelmechanism which is dominant in undoped quantum wells and at the temperatures greater than 50K. The measurement under an external transverse magnetic field (Voigt configuration) demonstrates that the spin relaxation times in three spatial directions are also controlled simultaneously by electric field. The "total" control of electron spin relaxation can only be observed in 111-oriented quantum wells. Finally, we also develop the model to interpret the experimental measurement of spin relaxation anisotropy depending on electric field in 111-oriented quantum wells.
Download or read book Spin Dynamics in the Presence of Spin orbit Interactions written by Xin Liu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the spin dynamics in a high-mobility two dimensional electron gas (2DEG) system with generic spin-orbit interactions (SOIs). We derive a set of spin dynamic equations which capture the purely exponential to the damped oscillatory spin evolution modes observed in different regimes of SOI strength. Hence we provide a full treatment of the D'yakonov-Perel's mechanism by using the microscopic linear response theory from the weak to the strong SOI limit. We show that the damped oscillatory modes appear when the electron scattering time is larger than half of the spin precession time due to the SOI, in agreement with recent observations. We propose a new way to measure the scattering time and the relative strength of Rashba and linear Dresselhaus SOIs based on these modes and optical grating experiments. We discuss the physical interpretation of each of these modes in the context of Rabi oscillation. In the finite temperature, We study the spin dynamics in the presence of impurity and electron-electron (e-e) scattering in a III-V semiconductor quantum well. Starting from the Keldysh formalism, we develop the spin-charge dynamic equation at finite temperature in the presence of inelastic scattering which provide a new approach to describe the spin relaxation from the weak to the strong spin-orbit coupling (SOC) regime. In the weak SOC regime, our theory shows that when the system is near the SU(2) symmetry point, because the spin relaxation due to DP mechanism is suppressed dramatically, the spin relaxation is dominated by the Elliott-Yafet (EY) mechanism in a wide temperature regime. The non-monotonic temperature dependence of enhanced-lifetime of spin helix mode is due to the competition between the DP and EY mechanisms. In the strong SOC regime, the our theory is consistent to the previous theoretical results at zero temperature.
Download or read book Electron Spin Resonance and Related Phenomena in Low Dimensional Structures written by Marco Fanciulli and published by Springer Science & Business Media. This book was released on 2009-08-24 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here is a discussion of the state of the art of spin resonance in low dimensional structures, such as two-dimensional electron systems, quantum wires, and quantum dots. Leading scientists report on recent advances and discuss open issues and perspectives.
Download or read book Spin orbit Coupling Effects in Two Dimensional Electron and Hole Systems written by Roland Winkler and published by Springer. This book was released on 2003-10-06 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first part provides a general introduction to the electronic structure of quasi-two-dimensional systems with a particular focus on group-theoretical methods. The main part of the monograph is devoted to spin-orbit coupling phenomena at zero and nonzero magnetic fields. Throughout the book, the main focus is on a thorough discussion of the physical ideas and a detailed interpretation of the results. Accurate numerical calculations are complemented by simple and transparent analytical models that capture the important physics.
Download or read book Growth Optimization and Characterization of High Mobility Two dimensional Electron Systems in AlAs Quantum Wells written by Shivaji Dasgupta and published by . This book was released on 2009 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Random Walk Approach to Spin Dynamics in a Two dimensional Electron Gas with Spin orbit Coupling written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We introduce and solve a semiclassical random walk (RW) model that describes the dynamics of spin polarization waves in zinc-blende semiconductor quantum wells. We derive the dispersion relations for these waves, including the Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the effects of an electric field applied parallel to the spin polarization wave vector. In agreement with calculations based on quantum kinetic theory [P. Kleinert and V.V. Bryksin, Phys. Rev. B 76, 205326 (2007)], the RW approach predicts that spin waves acquire a phase velocity in the presence of the field that crosses zero at a nonzero wave vector, q0. In addition, we show that the spin-wave decay rate is independent of field at q0 but increases as (q-q0)2 for q `"q0. These predictions can be tested experimentally by suitable transient spin grating experiments.
Download or read book Spin Orbit Interaction in AlGaAs GaAs P Type Quantum Wells A Possible Explanation of the Metal Insulator Transition Observed in Two Dimensional Hole Systems written by L. S. Golub and published by . This book was released on 2001 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have performed a calculation of the temperature dependence of the weak-localization correction to resistance in a AlGaAs/GaAs p-type quantum well. In such systems where the spin orbit coupling by far dominates the energy dispersion, we find that the spin relaxation time becomes comparable with the estimated value of the phase coherence time at sufficiently low temperatures and low hole densities. We wish to suggest this crossover between these different relaxation times as a possible explanation of the experimentally observed 'metal-insulator' transition in two- dimensional hole systems.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2540 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Measurement of Electron hole Friction in an N doped GaAs AlGaAs Quantum Well Using Optical Transient grating Spectroscopy written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We use phase-resolved transient grating spectroscopy to measure the drift and diffusion of electron-hole density waves in a semiconductor quantum well. The unique aspects of this optical probe allow us to determine the frictional force between a two-dimensional Fermi liquid of electrons and a dilute gas of holes. Knowledge of electron-hole friction enables prediction of ambipolar dynamics in high-mobility electron systems.
Download or read book Spin Dynamics of Carriers in Doped GaAs Quantum well Systems written by Jaswinder Singh Sandhu and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Dynamics and Spin Relaxation of Excitons in Gaas Algaas Quantum Wells written by Aviv Frommer and published by . This book was released on 1993 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Doppler Velocimetry of Current Driven Spin Helices in a Two Dimensional Electron Gas written by Luyi Yang and published by . This book was released on 2013 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spins in semiconductors provide a pathway towards the development of spin-based electronics. The appeal of spin logic devices lies in the fact that the spin current is even under time reversal symmetry, yielding non-dissipative coupling to the electric field. To exploit the energy-saving potential of spin current it is essential to be able to control it. While recent demonstrations of electrical-gate control in spin-transistor configurations show great promise, operation at room temperature remains elusive. Further progress requires a deeper understanding of the propagation of spin polarization, particularly in the high mobility semiconductors used for devices. This thesis presents the demonstration and application of a powerful new optical technique, Doppler spin velocimetry, for probing the motion of spin polarization at the level of 1 nm on a picosecond time scale. We discuss experiments in which this technique is used to measure the motion of spin helices in high mobility n-GaAs quantum wells as a function of temperature, in-plane electric field, and photoinduced spin polarization amplitude. We find that the spin helix velocity changes sign as a function of wave vector and is zero at the wave vector that yields the largest spin lifetime. This observation is quite striking, but can be explained by the random walk model that we have developed. We discover that coherent spin precession within a propagating spin density wave is lost at temperatures near 150 K. This finding is critical to understanding why room temperature operation of devices based on electrical gate control of spin current has so far remained elusive. We report that, at all temperatures, electron spin polarization co-propagates with the high-mobility electron sea, even when this requires an unusual form of separation of spin density from photoinjected electron density. Furthermore, although the spin packet co-propagates with the two-dimensional electron gas, spin diffusion is strongly suppressed by electron-electron interactions, leading to remarkable resistance to diffusive spreading of the drifting pulse of spin polarization. Finally, we show that spin helices continue propagate at the same speed as the Fermi sea even when the electron drift velocity exceeds the Fermi velocity of 107 cm s-1. We also use this phase-resolved Doppler velocimetry technique to perform the first simultaneous measurements of drift and diffusion of electron-hole packets in the same two-dimensional electron gas. The results that we obtain strongly violate the picture of electron-hole transport that is presented in the classic textbook treatments of ambipolar dynamics. We find that the rates of transport are controlled almost entirely by the intrinsic frictional force exerted between electrons and holes, rather than the interaction of carriers with phonons or impurities. From the experimental data we obtain the first measurement of the "Coulomb drag" friction between electrons and holes coexisting in the same two-dimensional layer. Moreover, we show that the frictional force thus obtained is in quantitative agreement with theoretically predicted values, which follow entirely from electron density, temperature and fundamental constants, i.e. no adjustable parameters. The understanding of ambipolar transport that we have achieved is an essential prerequisite to the design of those spintronic devices in which spin current is carried by the drift of polarized electrons and holes.
