Photocurrents in magnetic bilayers for ultrafast spinorbitronics

Time: Thursday, October 25th, 16:00
Speaker: Frank FREIMUTH, Julich

Spin photocurrents excited by femtosecond laser pulses bring spinorbitronics to ultrafast timescales. Using the Keldysh formalism we systematically identify mechanisms behind the generation of spin photocurrents and charge photocurrents by femtosecond laser pulses. Noncentrosymmetric crystals and inversion asymmetric magnetic bilayers exhibit several mechanisms of photocurrent generation that are absent in centrosymmetric systems. First, there is the circular photogalvanic effect [1,2]. While previous works on the circular photogalvanic effect have focused on nonmagnetic semiconductors, we will discuss the magnetic photogalvanic effect in metallic magnetic bilayers [3]. Second, when magnetic solids are excited by femtosecond laser pulses, superdiffusive spin currents are generated, which are converted into charge currents by the inverse spin Hall effect [4,5]. Third, laser pulses excite magnetization dynamics due to the inverse Faraday effect and the optical spintransfer torque, which we will discuss for Fe, Co and FePt [6]. This magnetization dynamics generates photocurrents, because electrical currents are pumped by the inverse spin‐orbit torque [7,8]. Fourth, we find that also demagnetization drives photocurrents due to the collapse of the exchange field [9]. Based on density‐functional theory calculations we investigate these effects in Co/Pt and Mn/W bilayers.

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[3] F. Freimuth et al., arXiv:1710.10480 (2017)
[4] T. Kampfrath et al., Nature Nanotechnology 8, 256 (2013)
[5] T. Seifert et al., Nature Photonics 10, 483 (2016)
[6] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 94, 144432 (2016)
[7] T. J. Huisman et al., Nature Nanotechnology 11, 455 (2016)
[8] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 92, 064415 (2015)
[9] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 95, 094434 (2017