Semiconductor spintronics

Abstract

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. While metal spintronics has already found its niche in the computer industry-giant magnetoresistance systems are used as hard disk read heads-semiconductor spintronics is yet to demonstrate its full potential. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent interaction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In view of the importance of ferromagnetic semiconductor materials, a brief discussion of diluted magnetic semiconductors is included. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field. 72.25.Rb, 75.50.Pp, PACS

Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

“…As mentioned before, the small value for D S leads to a relatively small value for λ S . The order of magnitude of this value can be confirmed by comparing the change of R nl with L. By fitting an exponential decay 13 to the two R nl values versus L for the data obtained at 4.2 K (see Table 1, fit not shown), we receive λ S ≈ 0.5 μm, which is in agreement with the order of magnitude of λ S obtained from our fitted τ S and D S . 26 With D S = D C ≈ 200 cm 2 s −1 and τ S ≈ 2 ns, we would receive a λ S of 1 order of magnitude larger.…”

“…13 For this purpose, the magnetic field is aligned in z-direction. The resulting spin dynamics are described with the one-dimensional Bloch equation for the spin accumulation μ⃗ s We would like to note that this value for τ S is the longest reported spin relaxation time on monolayer graphene.…”

Theory of spin relaxation in two-electron laterally coupled Si/SiGe quantum dots

“…[2][3][4] In GaAs-based qubits, which are the state of the art, the essential gate operations 1, 5,6 for quantum computation 7,8 have been demonstrated. [9][10][11][12][13][14][15][16][17][18] But GaAs possesses a serious handicap for coherent spin manipulations-the nuclear spins.…”

Spin edge states: An exact solution and oscillations of the spin current

“…The situation is favorable in InAs where the Rashba coupling is larger, ␣ R Ϸ 112.49 meV Å. 1 Despite the smaller effective mass, m ‫ء‬ = 0.026m 0 , in weak fields about B 0 = 0.1 T, we have ␥ = 0.45. As we see below such a coupling results in essential modifications in the spectrum and transport of spin edge state, measurable in experiment.…”

“…[1][2][3] Unlike the charge, the electron spin is double valued and identifies two system components, which can be separated as in the spin-Hall effect 4,5 or mixed via the spin-Coulomb drag. 6,7 There are different mechanisms, realizing SOI, 1 and the interplay between them produces another rich arena for study and potential applications in spintronics. 8,9 In two-dimensional electron systems ͑2DES͒ of the quantum-Hall-effect geometry, the extended edge state play a central role in understanding of transport phenomena.…”