Topological Dirac states in asymmetric Pb1-xSnxTe quantum wells

The electronic structure of lead-salt (IV-VI semiconductor) topological quantum wells (T-QWs) is investigated with analytical solutions of the effective 4x4 Dimmock k & BULL; p model, which gives an accurate description of the bands around the fundamental energy gap. Specific results for three-layer Pb1-xSnxTe nanostructures with varying Sn composition are presented and the main differences between topological and normal (N) QWs highlighted. A series of new features are found in the spectrum of T-QWs, in particular in asymmetric QWs where large (Rashba spin-orbit) splittings are obtained for the topological Dirac states inside the gap

Electron g factor anisotropy in asymmetric III-V semiconductor quantum wells

The electron effective g factor tensor in asymmetric III-V semiconductor quantum wells (AQWs) and its tuning with the structure parameters and composition are investigated with envelope-function theory and the 8 x 8k . p Kane model. The spin-dependent terms in the electron effective Hamiltonian in the presence of an external magnetic field are treated as a perturbation and the g factors g(perpendicular to)* and g(parallel to)*, for the magnetic field in the QW plane and along the growth direction, are obtained analytically as a function of the well width L. The effects of the structure inversion asymmetry (SIA) on the electron g factor are analyzed. For the g-factor main anisotropy Delta g = g(perpendicular to)*-g(parallel to)*. in AQWs, a sign change is predicted in the narrow well limit due to SIA, which can explain recent measurements and be useful in spintronic applications. Specific results for narrow-gap AlSb/InAs/GaSb and AlxGa1-xAsGaAs/AlyGa1-yAs AQWs are presented and discussed with the available experimental data; in particular InAs QWs are shown to not only present much larger g factors but also a larger g-factor anisotropy, and with the opposite sign with respect to GaAs QWs

A spin field effect transistor for low leakage current

In a spin field effect transistor, a magnetic field is inevitably present in the channel because of the ferromagnetic source and drain contacts. This field causes random unwanted spin precession when carriers interact with non-magnetic impurities. The randomized spins lead to a large leakage current when the transistor is in the ``off''-state, resulting in significant standby power dissipation. We can counter this effect of the magnetic field by engineering the Dresselhaus spin-orbit interaction in the channel with a backgate. For realistic device parameters, a nearly perfect cancellation is possible, which should result in a low leakage current.Comment: To appear in Physica E. The revised version has additional material which addresses the issue of which way the contacts should be magnetized in a Spin Field Effect Transistor. This was neither addressed in the previous version, nor in the upcoming journal pape

Rashba spin-orbit coupling and spin relaxation in silicon quantum wells

Silicon is a leading candidate material for spin-based devices, and two-dimensional electron gases (2DEGs) formed in silicon heterostructures have been proposed for both spin transport and quantum dot quantum computing applications. The key parameter for these applications is the spin relaxation time. Here we apply the theory of D'yakonov and Perel' (DP) to calculate the electron spin resonance linewidth of a silicon 2DEG due to structural inversion asymmetry for arbitrary static magnetic field direction at low temperatures. We estimate the Rashba spin-orbit coupling coefficient in silicon quantum wells and find the $T_{1}$ and $T_{2}$ times of the spins from this mechanism as a function of momentum scattering time, magnetic field, and device-specific parameters. We obtain agreement with existing data for the angular dependence of the relaxation times and show that the magnitudes are consistent with the DP mechanism. We suggest how to increase the relaxation times by appropriate device design.Comment: Extended derivations and info, fixed typos and refs, updated figs and data. Worth a re-downloa

Quantum dots based on spin properties of semiconductor heterostructures

The possibility of a novel type of semiconductor quantum dots obtained by spatially modulating the spin-orbit coupling intensity in III-V heterostructures is discussed. Using the effective mass model we predict confined one-electron states having peculiar spin properties. Furthermore, from mean field calculations (local-spin-density and Hartree-Fock) we find that even two electrons could form a bound state in these dots.Comment: 9 pages, 3 figures. Accepted in PRB (Brief Report) (2004

Shot noise and spin-orbit coherent control of entangled and spin polarized electrons

We extend our previous work on shot noise for entangled and spin polarized electrons in a beam-splitter geometry with spin-orbit (\textit{s-o}) interaction in one of the incoming leads (lead 1). Besides accounting for both the Dresselhaus and the Rashba spin-orbit terms, we present general formulas for the shot noise of singlet and triplets states derived within the scattering approach. We determine the full scattering matrix of the system for the case of leads with \textit{two} orbital channels coupled via weak \textit{s-o} interactions inducing channel anticrossings. We show that this interband coupling coherently transfers electrons between the channels and gives rise to an additional modulation angle -- dependent on both the Rashba and Dresselhaus interaction strengths -- which allows for further independent coherent control of the electrons traversing the incoming leads. We derive explicit shot noise formulas for a variety of correlated pairs (e.g., Bell states) and lead spin polarizations. Interestingly, the singlet and \textit{each} of the triplets defined along the quantization axis perpendicular to lead 1 (with the local \textit{s-o} interaction) and in the plane of the beam splitter display distinctive shot noise for injection energies near the channel anticrossings; hence, one can tell apart all the triplets, in addition to the singlet, through noise measurements. We also find that spin-orbit induced backscattering within lead 1 reduces the visibility of the noise oscillations, due to the additional partition noise in this lead. Finally, we consider injection of two-particle wavepackets into leads with multiple discrete states and find that two-particle entanglement can still be observed via noise bunching and antibunching.Comment: 30 two-column pages and 7 figure

Rashba spin precession in quantum Hall edge channels

Quasi--one dimensional edge channels are formed at the boundary of a two-dimensional electron system subject to a strong perpendicular magnetic field. We consider the effect of Rashba spin--orbit coupling, induced by structural inversion asymmetry, on their electronic and transport properties. Both our analytical and numerical results show that spin--split quantum--Hall edge channels exhibit properties analogous to that of Rashba--split quantum wires. Suppressed backscattering and a long spin life time render these edge channels an ideal system for observing voltage--controlled spin precession. Based on the latter, we propose a magnet--less spin--dependent electron interferometer.Comment: 7 pages, 6 figure

Higher order contributions to Rashba and Dresselhaus effects

We have developed a method to systematically compute the form of Rashba- and Dresselhaus-like contributions to the spin Hamiltonian of heterostructures to an arbitrary order in the wavevector k. This is achieved by using the double group representations to construct general symmetry-allowed Hamiltonians with full spin-orbit effects within the tight-binding formalism. We have computed full-zone spin Hamiltonians for [001]-, [110]- and [111]-grown zinc blende heterostructures (D_{2d},C_{4v},C_{2v},C_{3v} point group symmetries), which are commonly used in spintronics. After an expansion of the Hamiltonian up to third order in k, we are able to obtain additional terms not found previously. The present method also provides the matrix elements for bulk zinc blendes (T_d) in the anion/cation and effective bond orbital model (EBOM) basis sets with full spin-orbit effects.Comment: v1: 11 pages, 3 figures, 8 table

Anomalous Rashba spin splitting in two-dimensional hole systems

It has long been assumed that the inversion asymmetry-induced Rashba spin splitting in two-dimensional (2D) systems at zero magnetic field is proportional to the electric field that characterizes the inversion asymmetry of the confining potential. Here we demonstrate, both theoretically and experimentally, that 2D heavy hole systems in accumulation layer-like single heterostructures show the opposite behavior, i.e., a decreasing, but nonzero electric field results in an increasing Rashba coefficient.Comment: 4 pages, 3 figure

Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry

In semiconductor heterostructures, bulk and structural inversion asymmetry and spin-orbit coupling induce a k-dependent spin splitting of valence and conduction subbands, which can be viewed as being caused by momentum-dependent crystal magnetic fields. This paper studies the influence of these effective magnetic fields on the intersubband spin dynamics in an asymmetric n-type GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin plasmons using linear response theory. The so-called D'yakonov-Perel' decoherence mechanism is inactive for collective intersubband excitations, i.e., crystal magnetic fields do not lead to decoherence of spin plasmons. Instead, we predict that the main signature of bulk and structural inversion asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting of the spin plasmon dispersion. The importance of many-body effects is pointed out, and conditions for experimental observation with inelastic light scattering are discussed.Comment: 8 pages, 6 figure