Gian Salis

Measurement of Rashba and Dresselhaus spin–orbit magnetic fields

Spin–orbit coupling is a manifestation of special relativity. In the reference frame of a moving electron, electric fields transform into magnetic fields, which interact with the electron spin and lift the degeneracy of spin-up and spin-down states. In solid-state systems, the resulting spin–orbit fields are referred to as Dresselhaus and Rashba fields, depending on whether the electric fields originate from bulk or structure inversion asymmetry, respectively. Yet, it remains a challenge to determine the absolute value of both contributions in a single sample. Here, we show that both fields can be measured by optically monitoring the angular dependence of the electrons’ spin precession on their direction of motion with respect to the crystal lattice. Furthermore, we demonstrate spin resonance induced by the spin–orbit fields. We apply our method to GaAs/InGaAs quantum-well electrons, but it should be universally useful to characterize spin–orbit interactions in semiconductors, and therefore could facilitate the design of spintronic devices.

SU-8 for real three-dimensional subdiffraction-limit two-photon microfabrication

We report the inherent utility of two-photon-absorption (TPA) in the fabrication of real three-dimensional (3D) structures with subdiffraction-limit resolution, based on SU-8 as the threshold polymer media. We exploit the nonlinear velocity dependence of TPA photopolymerization as the shutter mechanism for disruptive 3D lithography. We show that low numerical aperture optics can be used for the rapid microfabrication of ultrahigh-aspect ratio photoplastic pillars, planes, and cage structures.

Direct mapping of the formation of a persistent spin helix

Spin–orbit interaction induces spin-polarization decay in semiconductor quantum wells. But this decay can be suppressed in favour of a helical spin mode by tuning the interaction. Optical pump–probe measurements provide direct evidence of the resulting helix—a signature that has so far only been inferred from transport measurements.

Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin-injection device

The nonlocal spin resistance is measured as a function of temperature in a Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin injection, the spin resistance is observed up to room temperature and decays exponentially with temperature at a rate of 0.018\,K

Gate-controlled spin-orbit interaction in a parabolic GaAs/AlGaAs quantum well.

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Signatures of dynamically polarized nuclear spins in all-electrical lateral spin transport devices

. Post-growth annealing at 440\,K increases the spin signal at low temperatures, but the decay rate also increases to 0.030\,K

Stray-field-induced modification of coherent spin dynamics

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Spin-injection spectra of CoFe/GaAs contacts: Dependence on Fe concentration, interface, and annealing conditions

. From measurements of the diffusion constant and the spin lifetime in the GaAs channel, we conclude that sample annealing modifies the temperature dependence of the spin transfer efficiency at injection and detection contacts. Surprisingly, the spin transfer efficiency increases in samples that exhibit minority-spin injection.

Role of linear and cubic terms for drift-induced Dresselhaus spin-orbit splitting in a two-dimensional electron gas

We study the tunability of the spin-orbit interaction in a two-dimensional electron gas with a front and a back gate electrode by monitoring the spin precession frequency of drifting electrons using time-resolved Kerr rotation. The Rashba spin splitting can be tuned by the gate biases, while we find a small Dresselhaus splitting that depends only weakly on the gating. We determine the absolute values and signs of the two components and show that for zero Rashba spin splitting the anisotropy of the spin-dephasing rate vanishes.

Variation of elastic scattering across a quantum well

The effect of nuclear spins in Fe/GaAs all-electrical spin-injection devices is investigated. At temperatures below 50 K, strong modifications of the non-local spin signal are found that are characteristic for hyperfine coupling between conduction electrons and dynamically polarized nuclear spins. The perpendicular component of the nuclear Overhauser field depolarizes electron spins near zero in-plane external magnetic field, and can suppress such dephasing when antialigned with the external field, leading to satellite peaks in a Hanle measurement. The features observed agree well with a Monte Carlo simulation of the spin diffusion equation including hyperfine interaction, and are used to study the nuclear spin dynamics and relate it to the spin polarization of injected electrons.