Optically Injected Spin Currents in Semiconductors

Bhat, Ravi; Sipe, J. E.

doi:10.1103/physrevlett.85.5432

Cited by 195 publications

(238 citation statements)

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“…It has also been shown that it can induce photocurrents. Here, however, in contrast to the well-known photocurrents caused by quantum interference of one-and two-photon absorption processes in two color light, [8][9][10][11] the photocurrent is due to quantum interference in the elementary one-photon absorption process.…”

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confidence: 84%

Observation of the orbital circular photogalvanic effect

et al. 2009

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We report on the observation of the circular photogalvanic effect in Si-metal-oxide-semiconductor fieldeffect transistors with inversion channel excited by terahertz radiation. We demonstrate that in spite of the fact that the photocurrent is caused by transfer of the photon angular momentum to free carriers, it is not due to spin orientation but has a pure orbital origin. It results from the quantum interference of different pathways contributing to the free-carrier absorption of monochromatic radiation. DOI: 10.1103/PhysRevB.79.121302 PACS number͑s͒: 78.40.Fy, 72.40.ϩw, 73.40.Qv, 78.20.Ϫe The spin of electrons and holes in solid-state systems is an intensively studied quantum mechanical property showing a large variety of interesting physical phenomena. One of the most frequently used and powerful methods of generation and investigation of spin polarization is optical orientation with circularly polarized light. 1 Besides purely optical phenomena such as circularly polarized photoluminescence, the optical generation of an unbalanced spin distribution in a semiconductor may lead to helicity-dependent photocurrents, e.g., circular photogalvanic effect ͑CPGE͒. 2-4 CPGE current is excited only by light of nonzero helicity and reverses its direction upon switching the sign of circular polarization. So far, the CPGE has only been detected in materials with strong spin-orbit coupling and described by microscopic mechanisms based on spin-related processes. [2][3][4] Here we report on the observation of the CPGE caused by absorption of terahertz radiation in Si-metal-oxidesemiconductor field-effect transistors ͑Si-MOSFETs͒. The experimental demonstration of the existence of a helicitysensitive photocurrent in Si-based structures is of particular interest. Silicon is characterized by a vanishingly small spinorbit coupling which makes spin-related mechanisms of the CPGE ineffective and, therefore, cannot account for the observed helicity-dependent photocurrent. Thus, an access in explaining the CPGE is required, involving mechanisms of pure orbital ͑spin-unrelated͒ origin. Here, we show that the CPGE in our structures is due to quantum interference of different pathways contributing to monochromatic radiation absorption. This effect has been predicted theoretically 5 ͑see also Refs. 6 and 7͒ but not observed so far. Quantum interference plays an important role in various transport and optical phenomena. It has also been shown that it can induce photocurrents. Here, however, in contrast to the well-known photocurrents caused by quantum interference of one-and two-photon absorption processes in two color light, 8-11 the photocurrent is due to quantum interference in the elementary one-photon absorption process.We study n-type MOSFETs prepared on miscut Si surfaces to reduce spacial symmetry and enable photocurrents at normal incidence. The surfaces of our samples are tilted by the angle = 9.7°͑sample 1͒ or = 10.7°͑sample 2͒ from the ͑001͒ plane around x ʈ ͓110͔. We note, that the point group describing the miscut trans...

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confidence: 84%

Observation of the orbital circular photogalvanic effect

et al. 2009

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“…19,20 Expressions such as (4) and (8) can also be written for carrier spin polarization and spin current. 22 The interference terms of these describe '1+2' spin control 21 and '1+2' spin current injection, 13 which can be written in terms of material response pseudotensors ζ ijkl…”

Section: Preliminariesmentioning

confidence: 99%

“…43,69 However, we neglect such nonlocal corrections, as has been the practice in previous calculations of coherent control effects. 11,13,19 The initial state is the "vacuum" |0 ; it corresponds to completely filled valence bands and empty conduction bands. If the Coulomb interaction were neglected in a two-band model consisting of valence (v) and conduction (c) bands, the final states would be of the form a † ck a vk |0 , where the operator a † nk creates an electron in an eigenstate of H B , a Bloch state |n, k with band index n and wavevector k. The photon momentum has been neglected, consistent with the long wavelength approximation.…”

Section: Modelmentioning

confidence: 99%

“…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%

“…28,29 Nevertheless, microscopic theories for the interband '1 + 2' processes in bulk semiconductors have until now predicted trivial intrinsic phases. 11,13,19,21 The photocurrent, for example, was predicted to be proportional to the sine of the relative phase parameter for all final energies. 11 Each of these theories use the independent particle approximation, in which the Coulomb attraction between the injected electron and hole is neglected.…”

Section: Introductionmentioning

confidence: 99%

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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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Spin‐dependent Transport of Carriers in Semiconductors

Winkler

2007

Handbook of Magnetism and Advanced Magnetic Materials

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This article reviews spin-dependent transport of carriers in homogenous threedimensional and two-dimensional semiconductors. We begin with a discussion of optical orientation of electron spins, which allows both the creation and detection of spin-polarized carriers in semiconductors. Then we review non-equilibrium spin flow including spin drift and diffusion caused by electric fields and concentration gradients. A controlled spin precession is possible both in external magnetic fields and in effective magnetic fields due to a broken inversion symmetry. Although the Coulomb interaction does not couple to the spin degree of freedom, it affects the spin-dependent transport via the spin Coulomb drag. In gyrotropic media, the optical creation of spin-oriented electrons gives rise to spin photocurrents, which reverse their direction when the radiation helicity is changed from left-handed to right-handed. The reverse process is possible, too, i.e., an electric current in a gyrotropic medium gives rise to a spin polarization in the bulk of the sample.

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Optically Injected Spin Currents in Semiconductors

Cited by 195 publications

References 17 publications

Observation of the orbital circular photogalvanic effect

Observation of the orbital circular photogalvanic effect

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

Spin‐dependent Transport of Carriers in Semiconductors

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