Person: Rashba, Emmanuel
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Rashba
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Emmanuel
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Rashba, Emmanuel
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Publication Edge Absorption Theory in Semiconductors(1962-10) Rashba, Emmanuel; Gurgenishvili, G.E.A theoretical explanation is given for anomalously high intensity of absorption edge bands related to defects.Publication Victor Valentinivich Eremenko: Early Days in Science(American Institute of Physics, 2017) Rashba, EmmanuelPublication Quenching of dynamic nuclear polarization by spin–orbit coupling in GaAs quantum dots(Nature Pub. Group, 2015) Nichol, John M.; Harvey, Shannon; Shulman, Michael D.; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel; Halperin, Bertrand; Yacoby, AmirThe central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spin–orbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electron–nuclear system, despite weak spin–orbit coupling in GaAs. Using Landau–Zener sweeps to measure static and dynamic properties of the electron spin–flip probability, we observe that the size of the spin–orbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spin–orbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spin–orbit coupling in central-spin systems.Publication Self-Consistent Measurement and State Tomography of an Exchange-Only Spin Qubit(Nature Publishing Group, 2013) Medford, James Redding; Beil, J.; Taylor, J. M.; Bartlett, S. D.; Doherty, A. C.; Rashba, Emmanuel; DiVincenzo, D. P.; Lu, H.; Gossard, A. C.; Marcus, CQuantum-dot spin qubits characteristically use oscillating magnetic or electric fields, or quasi-static Zeeman field gradients, to realize full qubit control. For the case of three confined electrons, exchange interaction between two pairs allows qubit rotation around two axes, hence full control, using only electrostatic gates. Here, we report initialization, full control, and single-shot readout of a three-electron exchange-driven spin qubit. Control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in less than 2 ns. Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified. The methods developed here are generally applicable to systems with state leakage, noisy measurements and non-orthogonal control axes.Publication Semiconductor physics: Electric fields drive spins(Nature Publishing Group, 2006) Rashba, EmmanuelElectron spins are traditionally manipulated by a resonant magnetic field, but spin–orbit coupling provides a better option of achieving spin operation, using a resonant electric field. A theoretical treatment now fills in the microscopic detail of this process.Publication Theory of electric dipole spin resonance in a parabolic quantum well(American Physical Society (APS), 2006) Efros, Al. L; Rashba, EmmanuelA theory of Electric Dipole Spin Resonance (EDSR), that is caused by various mechanisms of spin-orbit coupling, is developed as applied to free electrons in a parabolic quantum well. Choosing a parabolic shape of the well has allowed us to find explicit expressions for the EDSR intensity and its dependence on the magnetic field direction in terms of the basic parameters of the Hamiltonian. By using these expressions, we have investigated and compared the effect of specific mechanisms of spin orbit (SO) coupling and different polarizations of ac electric field on the intensity of EDSR. It is our basic assumption that the SO coupling energy is small compared with all different competing energies (the confinement energy, and the cyclotron and Zeeman energies) that allowed us to describe all SO coupling mechanisms in the framework of the same general approach. For this purpose, we have developed an operator formalism for calculating matrix elements of the transitions between different quantum levels. To make these calculations efficient enough and to derive explicit and concise expressions for the EDSR intensity, we have established a set of remarkable identities relating the eigenfrequencies and the angles defining the spatial orientation of the quantizing magnetic field B (θ, φ) . Applicability of these identities is not restricted by EDSR and we expect them to be useful for the general theory of parabolic quantum wells. The angular dependences of the EDSR intensity, found for various SO coupling mechanisms, show a fine structure consisting of alternating up- and down-cusps originating from repopulating different quantum levels and their spin sublevels. Angular dependences of the EDSR intensity are indicative of the relative contributions of the competing mechanisms of SO coupling. Our results show that electrical manipulating electron spins in quantum wells is generally highly efficient, especially by an in-plane ac electric field.Publication Spin Dynamics and Spin Transport(Springer Nature, 2005) Rashba, EmmanuelSpin-orbit (SO) interaction critically influences electron spin dynamics and spin transport in bulk semiconductors and semiconductor microstructures. This interaction couples electron spin to dc and ac electric fields. Spin coupling to ac electric fields allows efficient spin manipulating by the electric component of electromagnetic field through the electric dipole spin resonance (EDSR) mechanism. Usually, it is much more efficient than the magnetic manipulation due to a larger coupling constant and the easier access to spins at a nanometer scale. The dependence of the EDSR intensity on the magnetic field direction allows measuring the relative strengths of the competing SO coupling mechanisms in quantum wells. Spin coupling to an in-plane electric field is much stronger than to a perpendicular field. Because electron bands in microstructures are spin split by SO interaction, electron spin is not conserved and spin transport in them is controlled by a number of competing parameters, hence, it is rather nontrivial. The relation between spin transport, spin currents, and spin populations is critically discussed. Importance of transients and sharp gradients for generating spin magnetization by electric fields and for ballistic spin transport is clarified.Publication Theory of Spin Hall Conductivity in n-Doped GaAs(American Physical Society (APS), 2005) Engel, Hans-Andreas; Halperin, Bertrand; Rashba, EmmanuelWe develop a theory of extrinsic spin currents in semiconductors, resulting from spin-orbit coupling at charged scatterers, which leads to skew-scattering and side-jump contributions to the spin-Hall conductivity. Applying the theory to bulk n-GaAs, without any free parameters, we find spin currents that are in reasonable agreement with experiments by Kato et al.Publication Sum rules for spin Hall conductivity cancellation(American Physical Society (APS), 2004) Rashba, EmmanuelIt has been shown recently that the universal dc spin conductivity of two-dimensional electrons with a Rashba spin-orbit interaction is canceled by vertex corrections in a weak scattering regime. We prove that the zero bulk spin conductivity is an intrinsic property of the free-electron Hamiltonian and scattering is merely a tool to reveal this property in terms of the diagrammatic technique. When Zeeman energy is neglected, the zero dc conductivity persists in a magnetic field. Spin conductivity increases resonantly at the cyclotron frequency and then decays towards the universal value.Publication Spin currents, spin populations, and dielectric function of noncentrosymmetric semiconductors(American Physical Society (APS), 2004) Rashba, EmmanuelIn Maxwellian electrodynamics, specific properties of the responses to external fields are included in constitutive equations. For noncentrosymmetric semiconductors, spin conductivity can be expressed in terms of the contribution of electric-dipole transitions between spin-split spectrum branches to the dielectric function. In a dissipationless regime, a spin current driven by an external electric field is tantamount to a background current in an equilibrium system with a reduced symmetry. The importance of transients and gradients for efficient spin-flux injection is emphasized.