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Sujet de stage / Master 2 Internship

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Spin injection in 2-D interface states

Contact: VIRET Michel, , michel.viret@cea.fr, +33 1 69 08 71 60
Summary:
The subject aims at studying the spin to charge conversion by 2-D interface states with strong spin-orbit coupling.
Possibility of continuation in PhD: Oui
Deadline for application:28/03/2018

Full description:
Spintronics relies on the discrimination of spin up and down carriers originally generated by charge currents in metallic ferromagnets. Recent developments aim to get rid of this source of dissipation by manipulating pure spin currents without their charge counterpart. One convenient way of achieving this is to use the spin-orbit coupling (SOC) interaction in a non-magnetic heavy metal like Pt. The interaction relies on a preferential directional scattering of electrons of different spins resulting in the generation of a spin current transverse to a charge current called the Spin Hall Effect (SHE). As signals should eventually be read as voltages, it is important to efficiently convert spin into charge, which can also be done using the inverse Spin Hall effect. Very recently, another SOC effect based on the Rashba interaction was shown to be more efficient. The effect stems from the joint action of the SOC and built-in electric potentials in two-dimensional electron gases existing at surfaces, interfaces or semiconductor quantum wells. Lastly, similar physics is at play in topological insulators, materials which are insulating in the bulk but conducting at their surfaces due to broken symmetry inducing topological states.
The Inverse (Rashba) Edelstein Effect (IEE) was first demonstrated in 2013 in the Ag/Bi interface. We have confirmed the origin of this effect and also studied other 2-D gases like that at the LaAlO3/SrTiO3 interface. A 2D electron liquid appears between these two insulators when LaAlO3 is epitaxially grown on TiO2-terminated SrTiO3 along the [001] direction. Electrons are transferred to the interface to compensate for the polar discontinuity present between the two materials. A strong Rashba spin-orbit interaction also results from the breaking of inversion symmetry, whose strength can be tuned by applying an external electric field. Several measurements remain to be carried out in this system including in-plane dependences of the Rashba coefficient, tunneling of a pure spin current through the LaAlO3 barrier and the influence of the ferroelectric instability in doped SrTiO3. Some other systems can also be envisioned like interface states in topological insulators like the irridates SrIr2O4.
The ‘stage’ proposed here will consist in measuring these properties as spins are injected by ferromagnetic resonance and laser induced ultra-fast excitation of a ferromagnet. Both techniques are mastered in our laboratory and the latter is very promising as it can give very interesting information concerning time-resolved injection and spin lifetime. The LAO/STO samples come from the University of Geneva while irridates are synthesized in our group by Pulsed Laser Deposition.
Technics/methods used during the internship:
Pulsed laser deposition (PLD). Structural characterizations (X-ray and electron diffraction), near field microscopies (AFM). Optical magnetic imaging with second harmonics (SHG). Lasers (Nd-YAG, femto-second Ti:Al2O3 ). Magnetism (SQUID, VSM). Electronic transport measurements.

Laboratory
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