Direct Observation of Optically Injected Spin-Polarized Currents in Semiconductors

Hübner, Jens; Rühle, W. W.; Klude, M.; Hommel, D.; Bhat, Ravi; Sipe, J. E.; Driel, H. M. van

doi:10.1103/physrevlett.90.216601

Cited by 224 publications

(156 citation statements)

References 12 publications

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“…Murakami et al 4 and Sinova et al 5 have shown that an in-plane electric field can cause a spin current, leading to the "intrinsic spin-Hall effect". Another possibility for the injection of spin current is coherently controlled optical excitations between the valence and the conduction band, as predicted by Bhat and Sipe 6,7 and observed experimentally in bulk crystals 8,9 and quantum wells (QWs) 10 .…”

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confidence: 94%

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Spin current injection by intersubband transitions in quantum wells

Sherman

Najmaie

Sipe

2005

Applied Physics Letters

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We show that a pure spin current can be injected in quantum wells by the absorption of linearly polarized infrared radiation, leading to transitions between subbands. The magnitude and the direction of the spin current depend on the Dresselhaus and Rashba spin-orbit coupling constants and light frequency and, therefore, can be manipulated by changing the light frequency and/or applying an external bias across the quantum well. The injected spin current should be observable either as a voltage generated via the anomalous spin-Hall effect, or by spatially resolved pump-probe optical spectroscopy.Spin current is an interesting physical phenomenon in its own right, and could have application in the delivery and transfer of electron spins in spintronics devices. From a fundamental point of view, various issues raised in the theory of this effect are far from being satisfactorily settled. As was shown by Rashba 1 , a spin current exists even in the equilibrium state of a two-dimensional (2D) electron gas with spin-orbit (SO) coupling. The application of an external electric field has been suggested as a strategy for driving the system out of equilibrium and inducing a spin current exhibiting transport effects. Mal'shukov et al. 2 and Governale et al. 3 suggested applying a time-dependent bias across a semiconducting heterostructure, thus modulating the strength of the SO coupling and generating a spin current. Murakami et al. 4 and Sinova et al. 5 have shown that an in-plane electric field can cause a spin current, leading to the "intrinsic spin-Hall effect". Another possibility for the injection of spin current is coherently controlled optical excitations between the valence and the conduction band, as predicted by Bhat and Sipe 6,7 and observed experimentally in bulk crystals 8,9 and quantum wells (QWs) 10 .Here we show that a spin current can be injected in QWs by infrared (IR) light absorption, driving transitions between different subbands. The injection of spin-polarized electric current in QWs due to intersubband transitions caused by circularly polarized radiation has already been observed by Ganichev et al. 11 . In contrast, here we investigate a pure spin current, where electrons moving in opposite directions have opposite orientations of spins, not accompanied by a net electrical current. We show that the strength and direction of this pure spin current can be manipulated by modulating the SO coupling strength via applied bias 12 and/or adjusting the light frequency.As an example we consider the (011) GaAs QW, where the electron spins have a considerable out-of plane component, thus making possible the observation of the pure spin current by detecting the voltage generated via the anomalous spin-Hall effect 13,14 . The first two subbands in the well are typically separated by the energyhω 0 ≈ 100 meV; the exact value depends on the width of the QW, dopant concentration, and the boundary conditions. The SO Hamiltonian for the (011) QW, H SO = H D + H R , is the sum of a Dresselhaus term 15 , H D , originatin...

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confidence: 94%

“…Another possibility for observing the pure spin current is spatially resolved pump-probe spectroscopy, as applied by Hübner et al 9 and Stevens et al 10 to investigate the spin current injected by interband transitions. In those experiments the centers of the spin-up and spin-down of excited electron distribution were separated by approximately 20 nm.…”

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confidence: 99%

Spin current injection by intersubband transitions in quantum wells

Sherman

Najmaie

Sipe

2005

Applied Physics Letters

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“…Based on the spin pumping principle, 8,9 an alternating or inhomogeneous magnetic field as a spinpumping force could result in a pure spin current. Experimentally, Stevens et al 10 and Hubner et al 11 have independently realized the pure spin current by using the quantum interference of two-color laser fields with cross-linear polarization in ZnSe and GaAs semiconductors. The transport of spin current by magnons have been theoretically studied by several groups, 12-14 e.g., Meier et al 12 demonstrated that by using a finite length spin chain between magnetic reservoirs, pure spin current can be generated without the transport of electrical charge.…”

Section: Introductionmentioning

confidence: 99%

Equilibrium spin current through tunneling junctions

Wang

Chan

2006

Phys. Rev. B

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We study equilibrium pure spin current through tunnelling junctions at zero bias. The two leads of the junctions connected via a thin insulator barrier, can be either a ferromagnetic metal (FM) or a nonmagnetic high-mobility twodimensional electron gas (2DEG) with Rashba spin orbital interaction (RSOI) or Dresselhaus spin orbital interaction (DSOI). As a lead of a tunnelling junction, the isotropic RSOI or DSOI in 2DEG can give rise to an average effective planar magnetic field orthogonal or parallel to the current direction. It is found by the linear response theory that equilibrium spin current J can flow in the following three junctions, 2DEG/2DEG, 2DEG/FM, and FM/FM junctions, as a result of the exchange coupling between the magnetic moments, h l and hr, in the two electrodes of the junction, i.e., J ∼ h l × hr. An important distinction between the FM and 2DEG with RSOI (DSOI) lead is that in a strict one-dimensional case RSOI (DSOI) cannot lead to equilibrium spin current in the junction since the two spin bands are not spin-polarized as in a FM lead where Zeeman spin splitting occurs.Pacs numbers: 72.25.Dc, 71.70. Ej

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“…10 Interband '1 + 2' interference in unbiased semiconductors, which is our interest here, allows independent control of electrical current injection 11,12 and spin current injection. 13,14,15,16,17,18 Furthermore, in noncentrosymmetric semiconductors, it allows independent control of carrier populations (i.e., absorption) 19,20 and carrier spin polarization. 21, 22 In each scenario, the experimenter can control the interference by adjusting the phases of the two colors.…”

Section: Introductionmentioning

confidence: 99%

Excitonic effects on the two-color coherent control of interband transitions in bulk semiconductors

Bhat

Sipe

2005

Phys. Rev. B

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Quantum interference between one-and two-photon absorption pathways allows coherent control of interband transitions in unbiased bulk semiconductors; carrier population, carrier spin polarization, photocurrent injection, and spin current injection may all be controlled. We extend the theory of these processes to include the electron-hole interaction. Our focus is on photon energies that excite carriers above the band edge, but close enough to it so that transition amplitudes based on low order expansions in k are applicable; both allowed-allowed and allowed-forbidden two-photon transition amplitudes are included. Analytic solutions are obtained using the effective mass theory of Wannier excitons; degenerate bands are accounted for, but envelope-hole coupling is neglected. We find a Coulomb enhancement of two-color coherent control process, and relate it to the Coulomb enhancements of one-and two-photon absorption. In addition, we find a frequency dependent phase shift in the dependence of photocurrent and spin current on the optical phases.The phase shift decreases monotonically from π/2 at the band edge to 0 over an energy range governed by the exciton binding energy. It is the difference between the partial wave phase shifts of the electron-hole envelope function reached by one-and two-photon pathways.

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Direct Observation of Optically Injected Spin-Polarized Currents in Semiconductors

Cited by 224 publications

References 12 publications

Spin current injection by intersubband transitions in quantum wells

Spin current injection by intersubband transitions in quantum wells

Equilibrium spin current through tunneling junctions

Excitonic effects on the two-color coherent control of interband transitions in bulk semiconductors

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