Spin Direction Of Electrons Research Articles

Exciton-bound electron-spin relaxation

Exciton luminescence polarization studies in semiconductor quantum wells have revealed the coexistence of two main mechanisms of exciton-spin relaxation: a well-known direct relaxation with simultaneous electron and hole spin flip due to the electron-hole exchange interaction and an indirect one with sequential spin flips of the single particles. The rate of exciton-spin relaxation in this indirect channel is limited by the slower single-particle spin-flip rate, which is typically the electron one. In this work a theory of exciton-bound electron-spin dynamics driven by the spin-orbit splitting in the conduction band is presented. It is shown that the off-diagonal matrix element between optical active and inactive exciton states that differ only with regard to the electron spin direction represents an effective magnetic field that changes randomly as the exciton is elastically scattered and relaxes its spin. The exchange splitting between the optical active and inactive states acts as a constant external magnetic field, reducing the relaxation. The estimated rate of the bound electron spin flip agrees well with values obtained from previous fittings of the experimental data. Semiconductor heterostructures with real-space indirect excitons, for which the sequential spin-flip relaxation channel becomes the dominant one, are also briefly discussed together with the dependence of the relaxation time on the well width.

Spin asymmetries in inverse photoemission from PbS(100)

Angle-resolved spin-polarised inverse photoemission spectroscopy (ARSPIPES) has been used to study the electron-spin dependence of the photon intensity from non-magnetic samples. With the electron spin direction normal to the incidence plane and the electron wave vector k in the ΓXWK mirror plane, a spin asymmetry of up to 18% is observed from PbS(100).

Spin scattering in ferromagnetic thin films.

By combining parallel and transverse magnetoresistance measurements on thin films of Co and Ni, the contribution of spin scattering at the domain walls is separated from the anisotropic magnetoresistance (AMR). A model, based on the Larmor-precession-induced deviation of the conduction electron spin direction during domain-wall traversal is developed. By using a scattering probability which varies with the cosine of the angle between the carrier spin and the local exchange field (as used for giant magnetoresistance systems) it is possible to account for the amplitude of the measured magnetoresistive effect. \textcopyright{} 1996 The American Physical Society.

Influence of Finite Carrier Concentrations on the Electronic Spectrum of a Ferromagnetic Semiconductor

AbstractStarting from the atomic limit‐solution of the s‐f model a diagram technique is used to obtain the one‐particle spectrum of a ferromagnetic semiconductor, valid first of all for low carrier concentration n in the small bandwidth case. It turns out that the conduction band is split, due to the s‐f interaction, into two subbands for every electron spin direction. The lower edge of the lower ↑subband is shifted to higher energies with increasing band occupation explaining herewith recent experiments on EuO. The approximation fulfills the exactly calculable (n = 0, T = 0)‐limiting case.

Electronic quasiparticle spectrum of ferromagnetic semiconductors in the sf model

The sf model for ferromagnetic semiconductors-Coulomb interaction included, but with simplified f-f exchange-has been exactly solved in the limit W to 0 (W=band width) using a Green function technique. It turns out that the original s level is split by the sf interaction into six quasiparticle levels for each electron spin direction. Starting from the atomic limit, a calculation has been performed for a conduction band of finite width under the assumption that it contains only one electron. The temperature behaviour of the quasiparticles energies and their spectral weights (reduced densities of states) is discussed. It is shown that especially very near to the ferromagnetic saturation, the dependence of the spectral weights on the magnetisation of the localised f system gives rise to a spectacular redistribution of the density of states. Furthermore, for sf coupling constants g up to 1 eV, a small variation of g leads already to very strong shifts in weight between the different quasiparticle subbands. It turns out that the usual assumption that the conduction band is split into two spin-polarised subbands is only reasonable, if at all, for very small g values.