Datta-Das Spin Field Effect Transistor Research Articles

Effects of magnetic fields on the Datta-Das spin field-effect transistor

A Datta-Das spin field-effect transistor is built of a heterostructure with a Rashba spin-orbit interaction (SOI) at the interface (or quantum well) separating two possibly magnetized reservoirs. The particle and spin currents between the two reservoirs are driven by chemical potentials that are (possibly) different for each spin direction. These currents are also tuned by varying the strength of the SOI, which changes the amount of the rotation of the spins of electrons crossing the heterostructure. Here we investigate the dependence of these currents on additional Zeeman fields on the heterostructure and on variations of the reservoir magnetizations. In contrast to the particle current, the spin currents are not necessarily conserved; an additional spin polarization is injected into the reservoirs. If a reservoir has a finite (equilibrium) magnetization, then we surprisingly find that the spin current into that reservoir can only have spins which are parallel to the reservoir magnetization, independent of all the other fields. This spin current can be enhanced by increasing the magnetization of the other reservoir, and can also be tuned by the SOI and the various magnetic fields. When only one reservoir is magnetized then the spin current into the other reservoir has arbitrary tunable size and direction. In particular, this spin current changes as the magnetization of the other reservoir is rotated. The optimal conditions for accumulating spin polarization on an unpolarized reservoir are to either apply a Zeeman field in addition to the SOI, or to polarize the other reservoir.

Light-modulated spin precession in a two dimensional spin field effect transistor

Perfect spin precession in a two dimensional electron gas is the basis of the Datta-Das spin field effect transistor. However, in a two dimensional system this ideal spin precession can be washed out by the intersubband mixing effects induced by the Rashba spin–orbit interaction. Here, we propose by applying an off-resonant linearly polarized light a perfect spin modulation of conductance can be demonstrated in a two dimensional spin field effect transistor. This is because in a two dimensional electron gas due to the renormalization of the Rashba spin–orbit coupling strength and the hopping amplitude by the light, the intersubband mixing effects can be weakened. For an appropriate intensity of the light, the intersubband mixing effects are completely suppressed. These phenomena provide a promising way to design an optically-controlled spintronics device.

Effects of Different Lead Magnetizations on the Datta–Das Spin Field-Effect Transistor

A Datta-Das spin field effect transistor is built of a one-dimensional weak link, with Rashba spin orbit interactions (SOI), which connects two magnetized reservoirs. The particle and spin currents between the two reservoirs are calculated to lowest order in the tunneling through the weak link and in the wide-band approximation, with emphasis on their dependence on the origins of the `bare' magnetizations in the reservoirs. The SOI is found to generate magnetization components in each reservoir, which rotate in the plane of the electric field (generating the SOI) and the weak link, only if the `bare' magnetization of the other reservoir has a non-zero component in that plane. The SOI affects the charge current only if both reservoirs are polarized. The charge current is conserved, but the transverse rotating magnetization current is not conserved since the SOI in the weak link generates extra spin polarizations which are injected into the reservoirs.

Conductance of two-dimensional waveguide in presence of the Rashba spin-orbit interaction

By using the transfer matrix method, we investigated spin transport in some straight structures in presence of the Rashba spin-orbit interaction. It is proved that the interference of two spin states is the same as that in one-dimensional Datta-Das spin field-effect transistor. The conductance of these structures has been calculated. Conductance quantization is common in these waveguides when we change the Fermi energy and the width of the waveguide. Using a periodic system of quadrate stubs and changing the Fermi energy, a nearly square-wave conductance can be obtained in some regions of the Fermi energy.

Valley-based field-effect transistors in graphene

An analog of the Datta-Das spin field-effect transistor (FET) is investigated, which is all graphene and based on the valley degree of freedom of electrons/holes. The ``valley FET'' envisioned consists of a quantum wire of gapped graphene (channel) sandwiched between two armchair graphene nanoribbons (source and drain), with the following correspondence to the spin FET: valley (K and ${K}^{\ensuremath{'}}$) \ensuremath{\leftrightarrow} spin (up and down), armchair graphene nanoribbons \ensuremath{\leftrightarrow} ferromagnetic leads, graphene quantum wire \ensuremath{\leftrightarrow} semiconductor quantum wire, valley-orbit interaction \ensuremath{\leftrightarrow} Rashba spin-orbit interaction. The device works as follows. The source (drain) injects (detects) carriers in a specific valley polarization. A side gate electric field is applied to the channel and modulates the valley polarization of carriers due to the valley-orbit interaction, thus controlling the amount of current collected at the drain. The valley FET is characterized by (i) smooth interfaces between leads and the channel, (ii) strong valley-orbit interaction for electrical control of drain current, and (iii) vanishing interband valley-flip scattering. By its analogy to the spin FET, the valley FET provides a potential framework to develop low-power FETs for graphene-based nanoelectronics.

Proposal for a Datta-Das transistor in the quantum Hall regime

We propose a resonant spin-field-effect transistor for chiral spin-resolved edge states in the integer quantum Hall effect with Rashba spin-orbit interaction. It employs a periodic array of voltage-controlled top gates that locally modulate the Rashba spin-orbit interaction. Strong resonant spin-field effect is achieved when the array periodicity matches the inverse of the wave-vector difference of the two chiral states involved. Well-known techniques of separately contacting the edge states make it possible to selectively populate and read out the edge states, allowing full spin readout. The resonant nature of the spin-field effect and the adiabatic character of the edge states guarantee a high degree of robustness with respect to disorder. Our device represents the quantum Hall version of the all-electrical Datta-Das spin-field effect transistor.

Temperature dependence of the transport properties of spin field-effect transistors built with InAs and Si channels

We study the transport properties of the Datta–Das spin field-effect transistor built on InAs and Si. First, we demonstrate that the amplitude of the magnetoresistance oscillations as a function of the band mismatch between the ferromagnetic contacts and the semiconductor channel made of InAs decreases dramatically with increasing temperature. A shorter InAs channel is needed to create an InAs-based SpinFET which will operate at higher temperatures. Second, we show that the [100] orientation of the fin is preferable for silicon SpinFETs due to stronger modulation of the conductance as a function of spin–orbit interaction and magnetic field. Short silicon fins can be used for current modulation as a function of the conduction band mismatch between the channel and the ferromagnetic contacts only at relatively low temperatures. In contrast, longer silicon channels allow a TMR modulation at room temperature by changing the strength of the spin–orbit interaction through the gate bias.

Filtering and analyzing mobile qubit information via Rashba–Dresselhaus–Aharonov–Bohm interferometers

Spin-1/2 electrons are scattered through one or two diamond-like loops, made of quantum dots connected by one-dimensional wires, and subject to both an Aharonov-Bohm flux and (Rashba and Dresselhaus) spin-orbit interactions. With some symmetry between the two branches of each diamond, and with appropriate tuning of the electric and magnetic fields (or of the diamond shapes) this device completely blocks electrons with one polarization, and allows only electrons with the opposite polarization to be transmitted. The directions of these polarizations are tunable by these fields, and do not depend on the energy of the scattered electrons. For each range of fields one can tune the site and bond energies of the device so that the transmission of the fully polarized electrons is close to unity. Thus, these devices perform as ideal spin filters, and these electrons can be viewed as mobile qubits; the device writes definite quantum information on the spinors of the outgoing electrons. The device can also read the information written on incoming polarized electrons: the charge transmission through the device contains full information on this polarization. The double-diamond device can also act as a realization of the Datta-Das spin field-effect transistor.

Ballistic transport in extended Datta–Das spin field effect transistors

The model of the Datta–Das spin field effect transistor [S. Datta, B. Das, Appl. Phys. Lett. 56 (1990) 665] is extended in several respects: (1) the Rashba effect and Dresselhaus effect coexist; (2) the incoming and outgoing leads are both ferromagnetic; (3) the interfacial scattering and band mismatch are taken into account. By using the Griffith boundary conditions, the transmission coefficients and, thus, the Landauer–Büttiker conductance are obtained analytically. The transmission probability and conductance of the spin field effect transistor are studied in detail.

Analysis of the two-dimensional Datta–Das spin field effect transistor

An analytical expression is derived for the conductance modulation of a ballistic two-dimensional Datta–das spin field effect transistor (SPINFET) as a function of gate voltage. Using this expression, we show that the recently observed conductance modulation in a two-dimensional SPINFET structure does not match the theoretically expected result very well. This calls into question the claimed demonstration of the SPINFET and underscores the need for further careful investigation.

Conductance modulation of a nonballistic Datta–Das spin field effect transistor

A Datta–Das spin field effect transistor (FET) made of a nonballistic quantum wire with asingle transport channel is considered. Although there is no spin relaxation and the spinprecession is not influenced by elastic scattering, successful spin FET operation can still beprevented by the conductance fluctuations. The necessary condition for the desired spinFET operation is obtained.

Mesoscopic effects in a single-mode Datta-Das spin field-effect transistor

We study a single-mode Datta-Das spin field-effect transistor (SFET) in the presence (absence) of impurity scattering and external magnetic fields, and find interesting mesoscopic effects such as peak splitting, phase locking, and period halving. Experimental observation of these effects appears to be feasible in a single-mode SFET made of materials such as $\mathrm{In}\mathrm{Ga}\mathrm{As}∕\mathrm{In}\mathrm{Al}\mathrm{As}$.

Effect of bulk inversion asymmetry on the Datta-Das transistor

A model of the Datta-Das spin field-effect transistor is presented which, in addition to the Rashba interaction, takes into account the influence of bulk inversion asymmetry of zinc-blende semiconductors. In the presence of bulk inversion asymmetry, the conductance is found to depend significantly on the crystallographic orientation of the channel. We determine the channel direction optimal for the observation of the Datta-Das effect in GaAs and InAs-based devices.