guest ::
| Home > Publications database > Laser excitation of photocurrents in inversion asymmetric ferromagnets |
| Home > Publications database > Laser excitation of photocurrents in inversion asymmetric ferromagnets |
| Conference Presentation (Other) | FZJ-2017-07187 |
2017
Abstract: By breaking the inversion symmetry in crystals one enables several mechanisms for photocurrent generation, which otherwise would be forbidden by symmetry. First, there is the circular photogalvanic effect [1,2], which has recently attracted attention in noncentrosymmetric Weyl semimetals [3,4]. Since most previous works on the circular photogalvanic effect have focused on nonmagnetic semiconductors, in this talk we will discuss this effect in ferromagnetic metals. 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 [5,6]. Third, photocurrents are also generated when magnetization dynamics is excited by laser pulses, because magnetization dynamics pumps electrical currents due to the inverse spin‐orbit torque (ISOT) [7]. At small frequencies, i.e., under typical FMR conditions, the inverse spin‐orbit torque can be understood in terms of spin pumping combined with the spin Hall effect and in terms of the Rashba or Dresselhaus spin‐orbit fields [8,9,10,11]. However, when magnetic solids are excited by femtosecond laser pulses, additional effects set in, such as ultrafast demagnetization, which lead to new mechanisms for generating electrical currents in inversion asymmetric magnets. These photocurrents provide a new tool to probe magnetization dynamics at subpicosecond time scales. Using the Keldysh formalism we systematically identify mechanisms behind the generation of electrical currents in the range from FMR up to optical frequencies, discovering also several new effects. In particular, we find that not only precession of magnetization, but also demagnetization, drives photocurrents [12]. Based on DFT calculations we investigate these effects in Co/Pt and Mn/W bilayers and elucidate the role that spin‐currents play. The inverse Faraday effect (IFE) and the optical spin‐transfer torque (OSTT) can be used to excite magnetization dynamics by femtosecond laser pulses. We present ab‐initio calculations of IFE and OSTT in Fe, Co and FePt, compare the relative magnitude of IFE and OSTT in these materials and discuss the disorder dependence[13].[1] J. W. McIver et al., Nature Nanotechnology 7, 96 (2012) [2] S. D. Ganichev and W. Prettl, JPCM 15, R935 (2003) [3] H. Ishizuka et al., PRL 117, 216601 (2016) [4] Q. Ma et al., Nature Physics, DOI:10.1038/NPHYS4146 (2017) [5] T. Kampfrath et al., Nature Nanotechnology 8, 256 (2013) [6] T. Seifert et al., Nature Photonics 10, 483 (2016) [7] T. J. Huisman et al., Nature Nanotechnology 11, 455 (2016)[8] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 90, 174423 (2014) [9] F. Freimuth, S. Blügel and Y. Mokrousov, JPCM 26, 104202 (2014) [10] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 92, 064415 (2015) [11] F. Freimuth, S. Blügel and Y. Mokrousov, JPCM 28, 316001 (2016) [12] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 95, 094434 (2017) [13] F. Freimuth, S. Blügel and Y. Mokrousov, PRB 94, 144432 (2016)
|
The record appears in these collections: |