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Spin voltage generation through optical excitation of complementary spin populations

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Abstract

By exploiting the spin degree of freedom of carriers inside electronic devices, spintronics has a huge potential for quantum computation and dissipationless interconnects1. 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 rules2.

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Figure 1: Spin voltage generation and experimental set-up for spatially resolved inverse spin Hall effect (ISHE) measurements.
Figure 2: Measurement of optical spin injection and detection through ISHE.
Figure 3: Simulations and comparison with the experimental data.
Figure 4: Photon energy, excitation power and stripe width dependence of the ISHE signal.

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Acknowledgements

The authors would like to thank L. Duò for fruitful discussions. The CARIPLO foundation is acknowledged for partially funding this work through the NANOGAP (2010-0632) project. The research leading to these results has received funding from the European Union’s Seventh Framework Programme under grant agreement No 613055.

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Contributions

M.B. and G.I. fabricated the samples. F.B. and M.C. carried out the measurements. P.B. performed the numerical simulations. M.C., M.F. and F.C. provided the confocal apparatus with light polarization analysis. F.B. and M.C. performed the data analysis. F.C., G.I. and M.F. coordinated the entire work. All the authors contributed to the writing of the manuscript.

Corresponding author

Correspondence to Marco Finazzi.

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The authors declare no competing financial interests.

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Bottegoni, F., Celebrano, M., Bollani, M. et al. Spin voltage generation through optical excitation of complementary spin populations. Nature Mater 13, 790–795 (2014). https://doi.org/10.1038/nmat4015

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