Zero-bias spin separation

Ganichev, Sergey; Bel'kov, Vasily V.; Tarasenko, S. A.; Danilov, Sergey; Giglberger, Stephan; Hoffmann, Christoph; Ivchenko, E. L.; Weiss, Dieter; Wegscheider, Werner; Gerl, Christian; Schuh, Dieter; Stahl, Joachim; Boeck, Joan De; Borghs, Gustaaf; Prettl, Wilhelm

doi:10.1038/nphys390

Cited by 95 publications

(154 citation statements)

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“…Nevertheless, a finite pure spin current J spin = 1 2 ͑i +1/2 − i −1/2 ͒ is generated since electrons with spin-up and spindown move in opposite directions. 32 This leads to a spatial spin separation and spin accumulation at the edges of the sample. In the above analysis we do not consider the effect of a k-linear spin splitting of the electron subband since it does not lead to a significant contribution to the pure spin current.…”

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confidence: 99%

“…Spin currents recently attracted rapidly growing interest since they can provide new tools for the realization of all-electric nonmagnetic semiconductor spintronics. Various phenomena comprising charge photocurrents driven by the spin degree of freedom [18][19][20][21][22][23][24][25][26] and spin separation caused by pure spin currents [27][28][29][30][31][32] were reported. Most of these phenomena originate from the well known lifting of spin degeneracy.…”

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confidence: 99%

“…In gyrotropic media, such as low-dimensional GaAs structures or asymmetric SiGe QWs investigated here, however, spin-orbit interaction adds an asymmetric spin-dependent term to the scattering probability. 32 This term in the scattering matrix element is proportional to components of ͓ ϫ ͑k + kЈ͔͒, where is the vector composed of the Pauli matrices, k and kЈ are the initial and scattered electron wave vectors. 38 Due to spindependent scattering, transitions to positive and negative k x Ј states occur with different probabilities.…”

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confidence: 99%

“…30,31,[35][36][37] In contrast to the latter, no external bias needs to be applied. 32 Spin separation due to spin-dependent scattering in gyrotropic media can be achieved in various ways but all of them must drive the electron gas into a nonequilibrium state. One straightforward method used here is to heat the electron system by terahertz ͑THz͒ or microwave radiation.…”

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“…32 Drude absorption is caused by indirect intraband optical transitions and includes a momentum transfer from phonons or impurities to electrons to satisfy momentum conservation. Figure 1͑b͒ sketches the process of Drude absorption via virtual states for the spin-up subband.…”

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Pure spin currents induced by spin-dependent scattering processes in SiGe quantum well structures

et al. 2007

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We show that spin-dependent electron-phonon interaction in the energy relaxation of a two-dimensional electron gas results in equal and oppositely directed currents in the spin-up and spin-down subbands yielding a pure spin current. In our experiments on SiGe heterostructures the pure spin current is converted into an electric current applying a magnetic field that lifts the cancellation of the two partial charge flows. A microscopic theory of this effect, taking account of the asymmetry of the relaxation process, is developed and is in good agreement with the experimental data. DOI: 10.1103/PhysRevB.75.155317 PACS number͑s͒: 73.21.Fg, 72.25.Fe, 78.67.De, 73.63.Hs Lately, there has been much interest in the use of the spin of carriers in semiconductor quantum well ͑QW͒ structures together with their charge to realize concepts such as spintronics and spin-optoelectronics. 1 The transport of the spin of charge carriers in semiconductor nanostructures is one of the key problems in this field. Among the necessary conditions to realize spintronics devices there are a high spin polarization in QWs and a large spin splitting of subbands. The latter is important to control spins by an external electric field via the Rashba effect. 2 While most of the investigations aimed at spintronics and spin-optoelectronics have been carried out on III-V compounds, some recent results obtained on nonmagnetic SiGe nanostructures applying electron spin resonance 3,4 ͑ESR͒ and the circular photogalvanic effect ͑CPGE͒, 5,6 demonstrated that this material may be a promising system for spin-based electronics. ESR and CPGE data show that spin relaxation times in SiGe QWs can be sufficiently long, 3,4,[7][8][9][10][11] that the spin degeneracy is lifted, 3,5,6,11,12 that the g factor is tunable by crystallographic direction, electron density, Ge content, kinetic energy of free carriers, and electric current 3,13-17 and that spin manipulation can be achieved by means of the spin-echo method. 4 Here we report on an electrically measured observation of pure spin currents causing spatial spin separation in SiGe quantum well structures, allowing manipulation of spins in this material which is attractive for high-speed electronics and spintronics. Spin currents recently attracted rapidly growing interest since they can provide new tools for the realization of all-electric nonmagnetic semiconductor spintronics. Various phenomena comprising charge photocurrents driven by the spin degree of freedom 18-26 and spin separation caused by pure spin currents 27-32 were reported. Most of these phenomena originate from the well known lifting of spin degeneracy. The latter causes the band structure to split into spin-up and spin-down branches described by linear in wave vector k terms in the Hamiltonian due to structure inversion asymmetry ͑SIA͒ or bulk inversion asymmetry ͑BIA͒. The pure spin currents reported here are caused by less known spin-dependent electron scattering processes 33,34 which generate a pure spin current, causing spin separation in a ...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Pure spin currents induced by spin-dependent scattering processes in SiGe quantum well structures

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Bulk Rashba Semiconductors and Related Quantum Phenomena

Bahramy

Ogawa

2017

Advanced Materials

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zone (BZ) unless it is protected by a special crystalline symmetry. If the breaking of IS is such that the electrons feel a net gradient of potential normal to their momentum direction, the SOI results in a situation where every electron's spin is locked perpendicular to its momentum (see Figure 1). This phenomenon is called the Rashba effect [2,3] and is known to be responsible for many novel quantum phenomena such as spin Hall and Edelstein effects, [4,5] spin galvanic effect, [6] magnetoelectric effect, [7] and non-centrosymmetric superconductivity. [8] Although the Rashba effect has been known for more than sixty years, it has been mainly sought for in two-dimensional (2D) electronic systems, such as the semiconductor heterostructures [9] and the surface/interface of noble and heavy metals. [10] This is because the general rationale has been that the bulk systems can not exhibit a sizable Rashba spin splitting (RSS) due to the internal constraints such as the electric dipole screening. The recent angle-resolved photoemission spectroscopy (ARPES) study by Ishizaka et al. has, however, proven that this picture is not always true. [11] Their ARPES data, backed by the first principles calculations, [12] have revealed that in the polar semiconductor BiTeI, the bulk states exhibit an extremely large RSS. In fact, the RSS observed in bulk BiTeI has been shown [11] to exceed the largest RSS realized in a 2D system. [10] Further ARPES experiments [13][14][15][16][17] and ab initio calculations [18] have unveiled the similar effect in the other bismuth tellurohallides (BiTeBr and BiTeCl) and even in some ferroelectric semiconductors such as GeTe. [19,20] In all these systems, it turns out that the bulk RSS originates from an anomalous ordering of the conduction and/or valence bands combined with the strong SOI and narrowness of the band gap. [12] The bulk RSS has also been shown to lead to a variety of quantum effects in BiTeX (X = Cl, Br and I) compounds such as unique optical transitions, [21] strong magnetooptical responses, [22] a divergent orbital dia-/para-magnetism, [23] zero-bias magneto-and galvanic photocurrent [24,25] and a nontrivial Berry's phase. [26] Moreover, it has been theoretically proposed [27] and indications have been experimentally reported [28,29] that these systems may turn into a topological insulator under the application of a hydrostatic pressure. Together, these effects indicate that bulk RSS provide a new route to manipulate the spin degree of freedom of electrons, and BiTeX, as Bithmuth tellurohalides BiTeX (X = Cl, Br and I) are model examples of bulk Rashba semiconductors, exhibiting a giant Rashba-type spin splitting among their both valence and conduction bands. Extensive spectroscopic and transport experiments combined with the state-of-the-art first-principles calculations have revealed many unique quantum phenomena emerging from the bulk Rashba effect in these systems. The novel features such as the exotic inter-and intra-band optical transitions, enhanced magneto-optical response...

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High‐Frequency Nonlinear Transport and Photogalvanic Effects in 2D Topological Insulators

Durnev

Tarasenko

2019

Annalen der Physik

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Excitation of a topological insulator by a high-frequency electric field of a laser radiation leads to a dc electric current in the helical edge channel whose direction and magnitude are sensitive to the radiation polarization and depend on the physical properties of the edge. An overview of theoretical and experimental studies of such edge photoelectric effects in 2D topological insulators based on semiconductor quantum wells is presented. First, a phenomenological description is given of edge photocurrents, which may originate from the photogalvanic effects or the photon drag effects, for edges of all possible symmetry. Then, microscopic mechanisms of photocurrent generation for different types of optical transitions involving helical edge states are discussed. They include direct and indirect optical transitions within the edge channel and edge-to-bulk optical transitions.

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Zero-bias spin separation

Cited by 95 publications

References 11 publications

Pure spin currents induced by spin-dependent scattering processes in SiGe quantum well structures

Pure spin currents induced by spin-dependent scattering processes in SiGe quantum well structures

Bulk Rashba Semiconductors and Related Quantum Phenomena

High‐Frequency Nonlinear Transport and Photogalvanic Effects in 2D Topological Insulators

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