Spin susceptibilities, spin densities, and their connection to spin currents

Erlingsson, Sigurdur I.; Schliemann, John; Loss, Daniel

doi:10.1103/physrevb.71.035319

Cited by 77 publications

(113 citation statements)

References 43 publications

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“…that is similar to the mass and charge currents and is widely used, lacks the proper justification for systems with SO coupling [27,28,29,31]; here i, j are Cartesian coordinates. To the best of my knowledge, no experiments for measuring the quantities defined by Eq.…”

Section: Spin Transport In Media With Spin-orbit Coupling: Spin Flux mentioning

confidence: 99%

Spin Dynamics and Spin Transport

Rashba

2005

J Supercond

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Spin-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.

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Section: Spin Transport In Media With Spin-orbit Coupling: Spin Flux mentioning

confidence: 99%

Spin Dynamics and Spin Transport

Rashba

2005

J Supercond

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“…Recently, there are emerging theoretical interests on the spin Hall effect in a spin-orbit coupled system [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. The spin Hall effect refers to a non-zero spin current in the direction transverse to the direction of the applied electric field.…”

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confidence: 99%

Intrinsic Spin and Orbital Angular Momentum Hall Effect

2005

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A generalized definition of intrinsic and extrinsic transport coefficients is introduced. We show that transport coefficients from the intrinsic origin are solely determined by local electronic structure, and thus the intrinsic spin Hall effect is not a transport phenomenon. The intrinsic spin Hall current is always accompanied by an equal but opposite intrinsic orbital-angular-momentum Hall current. We prove that the intrinsic spin Hall effect does not induce a spin accumulation at the edge of the sample or near the interface.PACS numbers: 72.15.Gd, 73.50.Jt Recently, there are emerging theoretical interests on the spin Hall effect in a spin-orbit coupled system [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. The spin Hall effect refers to a non-zero spin current in the direction transverse to the direction of the applied electric field. Earlier studies had been focused on an extrinsic effect [15,16], namely, when conduction electrons scatter off an impurity with the spin-orbit interaction, the electrons tend to deflect to the left (right) more than to the right (left) for a given spin orientation of the electrons. Thus the impurity is the prerequisite in the extrinsic spin Hall effect. Recently, the spin Hall effect has been extended to semiconductor heterostructures where the spin-orbit coupled bands are important. It has been shown that the spin current exists in the absence of impurities, termed as the intrinsic or dissipationless spin Hall effect (ISHE) in order to distinguish the impurity-driven extrinsic spin Hall effect (ESHE) mentioned above. In general, the magnitude of ISHE is two to three orders larger than that of ESHE; this immediately generates an explosive interest in theoretical research on the ISHE since the spin current is regarded as one of the key variables in spintronics application.However, the spin current generated via ISHE is fundamentally different from conventional spin-polarized transport in many ways. First, the spin current is carried by the entire spin-orbit coupled Fermi sea, not just electrons or holes at the Fermi level [1,4]. Second, ISHE exists even for an equilibrium system (without external electric fields) [5] and ISHE is closely related to the dielectric response function that characterizes the electronic deformation [6]. Most recently, it is proposed that the intrinsic spin Hall effect exists even in insulators [17]. The above unconventional properties cast serious doubts on experimental relevance of the intrinsic spin current. It has been already alerted by Rashba [5,6] that the ISHE may not be a transport phenomenon. Due to the ill-defined nature of the spin current in the spin-orbit coupled Hamiltonian, theories utilizing different approaches produce contradicting results: some predicted a zero spin Hall current in the presence of an arbitrary weak disorder and some claimed a universal spin conductivity at weak disorder. In this letter, we do not try to resolve the above theoretical debate, instead we reveal the spurious nature of the intrinsic spin Hall effect and discuss i...

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“…To quantify the spin current density J ab , we use the conventional [14,15] single particle spin current operator…”

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confidence: 99%

Generation of Spin Currents via Raman Scattering

2005

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We show theoretically that stimulated spin flip Raman scattering can be used to inject spin currents in doped semiconductors with spin split bands. A pure spin current, where oppositely oriented spins move in opposite directions, can be injected in zincblende crystals and structures. The calculated spin current should be detectable by pump-probe optical spectroscopy and anomalous Hall effect measurement.PACS numbers: 71.70.Ej Spintronics is the strategy of using the spins of carriers in solid state structures as a new degree of freedom to carry and transform information [1]. An important capability is the generation of spin currents, which couple spin and charge. Suggestions for the generation of spin currents have included proposals based on the use of the extrinsic and intrinsic spin Hall effects, as well as spin pumping [2,3,4]. All-optical generation and control of spin currents have also been proposed and observed [5,6,7,8,9]. In these optical schemes, the generation of the spin current is accompanied by the deposition of photon energies of about 1 eV per carrier in the system. Most of this energy is used simply to generate the electron-hole pairs, and is lost in the sense that it does not contribute to the motion of the carriers. An obvious goal for the alloptical manipulation of spin is the minimization of such energy loss.Here we propose a new scheme for generating spin currents in doped semiconductors via a two photon Raman scattering process [10,11], which can be understood as the absorption of a photon of frequency ω 1 and the emission of a photon at ω 2 . This process deposits an energy ofhΩ =h (ω 1 − ω 2 ) per carrier in the crystal, which for GaAs is only about 0.5 meV. In the presence of spin splitting of the bands, stimulated spin-flip Raman scattering can produce a pure spin current, where electrons with opposite spins move in opposite directions. Hence no net charge current is injected.Crucial to this effect is the spin-splitting of states, which results from the lack of inversion symmetry of the crystal. A schematic picture of the conduction states is shown in Fig. 1, where E F denotes the Fermi energy. For simplicity we take the temperature to be zero [12]. The proposal in this letter is based on optically inducing transitions between states d(±k) and u(±k) at ±k wavevectors, as depicted in Fig. 1, via Raman scattering. As an example, we first consider an optical field E = E(ω 1 )e −iω1t + E(ω 2 )e −iω2t + c.c. in the material, where c.c. denotes complex conjugation and ω 1 > ω 2 and then present an experimentally relevant scenario of pulse excitation. The interaction of this field with the crystal in the dipole approximation is described by H int = −(e/mc)p · A(t), where e(m) is the charge(mass) of an electron, c is the speed of light and A(t) is the vector potential associated with the field. In the ground state |0 , electrons occupy states up to the Fermi level. The wavefunction of the perturbed system at time t is then written as |Ψ(t) = c 0 (t)|0 + k c k (t)|ehk , where |ehk , denote...

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Spin susceptibilities, spin densities, and their connection to spin currents

Cited by 77 publications

References 43 publications

Spin Dynamics and Spin Transport

Spin Dynamics and Spin Transport

Intrinsic Spin and Orbital Angular Momentum Hall Effect

Generation of Spin Currents via Raman Scattering

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