Spin voltage generation through optical excitation of complementary spin populations

Abstract

By exploiting the spin degree of freedom of carriers inside electronic devices, spintronics has a huge potential for quantum computation and dissipationless interconnects. Pure spin currents in spintronic devices should be driven by a spin voltage generator, able to drive the spin distribution out of equilibrium without inducing charge currents. Ideally, such a generator should operate at room temperature, be highly integrable with existing semiconductor technology, and not interfere with other spintronic building blocks that make use of ferromagnetic materials. Here we demonstrate a device that matches these requirements by realizing the spintronic equivalent of a photovoltaic generator. Whereas a photovoltaic generator spatially separates photoexcited electrons and holes, our device exploits circularly polarized light to produce two spatially well-defined electron populations with opposite in-plane spin projections. This is achieved by modulating the phase and amplitude of the light wavefronts entering a semiconductor (germanium) with a patterned metal overlayer (platinum). The resulting light diffraction pattern features a spatially modulated chirality inside the semiconductor, which locally excites spin-polarized electrons thanks to electric dipole selection rules.

Ultrafast valley relaxation dynamics in monolayerMoS2probed by nonequilibrium optical techniques

“…Exploiting and manipulating the spin and valley degrees of freedom in order to process and store information is one of the most challenging goals of modern solid-state physics, and already resulted in the demonstration of several functional devices [1][2][3][4][5][6]. In this context, transition metal dichalcogenides (TMDs) add novel functionalities, due to the strong interplay between the spin and the crystal momentum of the carriers [7], and represent a promising platform to develop new spin and valleytronic devices thanks to their peculiar electronic structure [8] and the integrability with graphene technology [9,10].…”

Pure spin currents in Ge probed by inverse spin-Hall effect

“…36 A sharp decrease is instead detected when approaching hν = 1.1 eV due to the fact that photon energies well above the SO threshold are achieved. 35,37 Then, for hν > E d + ∆E so , the signal goes to zero, consistently with the photon energy dependence of the electron spin polarization P. 36 The hν-dependence of the experimental data can be explained by taking into account a onedimensional spin-drift diffusion model. 38 In this respect, we have numerically solved the spin driftdiffusion equations for spin and charge at the Pt/Ge Schottky junction.…”

Optical Orientation and Inverse Spin Hall Effect as Effective Tools to Investigate Spin-Dependent Diffusion

“…On the other hand, the SO splitting is much larger in semiconductors such as Ge and GaAs, which are characterized by a higher atomic number Z than Si (∆ Ge ≈ 0.29 eV and ∆ GaAS ≈ 0.34 eV, respectively), allowing the excitation of an electron population in the conduction band of these semiconductors with a spin polarization P that can be as high as 50% for bulk materials [9,10], but that can reach even higher values in low symmetry systems where the HH-LH degeneracy is removed by e.g., strain [11][12][13] or reduced dimensionality [14]. In addition to allowing the generation of much higher spin polarizations in semiconductors as compared with all-electrical spin-injection schemes, spin orientation can also be exploited to create a spatially-modulated spin voltage beneath a patterned overlayer and to realize the spin analogue of a photovoltaic generator [15].…”