Local spin valve effect in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report on a local spin valve effect observed unambiguously in lateral all-semiconductor all-electrical spin injection devices, employing p+-(Ga,Mn)As/n+-GaAs Esaki diode structures as spin aligning contacts. We discuss the observed local spin-valve signal as a result of interplay between spin-transport-related contribution and tunneling anisotropic magnetoresistance of magnetic contacts. The magnitude of the spin-related magnetoresistance change is equal to 30 Ohm which is twice the magnitude of the measured non-local signal.Comment: submitted to Appl. Phys. Let

Tunneling Anisotropic Spin Polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report here on anisotropy of spin polarization obtained in lateral all-semiconductor all-electrical spin injection devices, employing $p^{+}-$(Ga,Mn)As/$n^{+}-$GaAs Esaki diode structures as spin aligning contacts, resulting from the dependence of the efficiency of spin tunneling on the orientation of spins with respect to different crystallographic directions. We observed an in-plane anisotropy of $~8$ in case of spins oriented either along $[1\bar{1}0]$ or $[110]$ directions and $~25$ anisotropy between in-plane and perpendicular-to-plane orientation of spins.Comment: 9 pages, 3 figure

All-electrical measurements of direct spin Hall effect in GaAs with Esaki diode electrodes

We report on measurements of direct spin Hall effect in a lightly n-doped GaAs channel. As spin detecting contacts we employed highly efficient ferromagnetic Fe/(Ga,Mn)As/GaAs Esaki diode structures. We investigate bias and temperature dependence of the measured spin Hall signal and evaluate the value of total spin Hall conductivity and its dependence on channel conductivity and temperature. From the results we determine skew scattering and side jump contribution to the total spin hall conductivity and compare it with the results of experiments on higher conductive n-GaAs channels[Phys. Rev. Lett. 105,156602(2010)]. As a result we conclude that both skewness and side jump contribution cannot be fully independent on the conductivity of the channel.Comment: 14 pages, 4 figure

Controlled rotation of electrically injected spins in a non-ballistic spin field-effect transistor

Electrically controlled rotation of spins in a semiconducting channel is a prerequisite for the successful realization of many spintronic devices, like, e.g., the spin field effect transistor (sFET). To date, there have been only a few reports on electrically controlled spin precession in sFET-like devices. These devices operated in the ballistic regime, as postulated in the original sFET proposal, and hence need high SOC channel materials in practice. Here, we demonstrate gate-controlled precession of spins in a non-ballistic sFET using an array of narrow diffusive wires as a channel between a spin source and a spin drain. Our study shows that spins traveling in a semiconducting channel can be coherently rotated on a distance far exceeding the electrons mean free path, and spin-transistor functionality can be thus achieved in non-ballistic channels with relatively low SOC, relaxing two major constraints of the original sFET proposal.Comment: Main text: 21 pages, 4 figures. Supplementary Information:11 pages, 4 figure

Shot Noise Induced by Nonequilibrium Spin Accumulation

When an electric current passes across a potential barrier, the partition process of electrons at the barrier gives rise to the shot noise, reflecting the discrete nature of the electric charge. Here we report the observation of excess shot noise connected with a spin current which is induced by a nonequilibrium spin accumulation in an all-semiconductor lateral spin-valve device. We find that this excess shot noise is proportional to the spin current. Additionally, we determine quantitatively the spin-injection-induced electron temperature by measuring the current noise. Our experiments show that spin accumulation driven shot noise provides a novel means of investigating nonequilibrium spin transport.Comment: 5 pages and Supplemental Materia

Nonuniform current density and spin accumulation in a 1 {\mu}m thick n-GaAs channel

The spin accumulation in an n-GaAs channel produced by spin extraction into a (Ga,Mn)As contact is measured by cross-sectional imaging of the spin polarization in GaAs. The spin polarization is observed in a 1 \mum thick n-GaAs channel with the maximum polarization near the contact edge opposite to the maximum current density. The one-dimensional model of electron drift and spin diffusion frequently used cannot explain this observation. It also leads to incorrect spin lifetimes from Hanle curves with a strong bias and distance dependence. Numerical simulations based on a two-dimensional drift-diffusion model, however, reproduce the observed spin distribution quite well and lead to realistic spin lifetimes

Hanle spin precession in a two-dimensional electron system

We investigate the nonlocal Hanle effect in high mobility two-dimensional electron systems using (Ga,Mn)As/GaAs spin Esaki diodes as spin selective contacts. Spin signals in these systems can be strongly affected by dynamic nuclear polarization, which mimics long spin-relaxation times extracted from the measured Hanle curves. Here, we introduce a method which largely suppresses these effects by using an ac injection-detection setup. This allows us to extract from the measurements realistic spin lifetimes on the order of single nanoseconds. As the detection of Hanle signals is also strongly affected by offset signals we discuss the magnetic field dependence of these background voltages observed in lateral nonlocal spin injection devices. We show how the strength of the background magnetoresistance can be minimized by choosing a proper device geometry

In-plane tunneling anisotropic magnetoresistance in (Ga,Mn)As/GaAs Esaki diodes in the regime of the ecxess current

We investigate the angular dependence of the tunneling anisotropic magnetoresistance in (Ga,Mn)As/n-GaAs spin Esaki diodes in the regime where the tunneling process is dominated by the excess current through midgap states in (Ga,Mn)As. We compare it to similar measurements performed in the regime of band-to-band tunneling. Whereas the latter show biaxial symmetry typical for magnetic anisotropy observed in (Ga,Mn)As samples, the former is dominated by uniaxial anisotropy along the 〈110〉 axes

Spatial variation of dynamic nuclear spin polarization probed by the non-local Hanle effect

The spatial distribution of dynamic nuclear spin polarization (DNP) has been investigated in a lateral all-semiconductor spin-injection device based on a (Ga,Mn)As/n þ -GaAs spin-Esaki diode. The DNP induced by the hyperfine interaction has been probed via satellite peaks in non-local Hanle-type spin precession signals, indicating the recovery of electron spin polarization. A quantitative analysis using the self-consistent calculation reproduces the magnetic field position of the satellite peaks as a function of spin injection bias and injector-detector separation. The distance dependence of the Hanle curves reveals that the spin-lattice relaxation rather than the hyperfine interaction is the dominant mechanism of nuclear spin relaxation in the non-local region

Dynamic nuclear spin polarization in an all-semiconductor spin injection device with (Ga,Mn)As/n-GaAs spin Esaki diode

We investigate the dynamic nuclear spinpolarization in an n-GaAs lateral channel induced by electrical spin injection from a (Ga,Mn)As/n-GaAs spin Esaki diode. Signatures of nuclear spinpolarization are studied in both three-terminal and non-local voltage signals, where a strong electron spin depolarization feature is observed close to zero magnetic field. This is due to the large nuclear field induced in the channel through hyperfine interaction between injected electron spins and localized nuclear spins. We study the time evolution of the dynamic nuclear spinpolarization and evaluate polarization and relaxation times of nuclear spins in the channel