Wave-diffusion theory of spin transport in metals after ultrashort-pulse excitation

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2012-06, Vol.85 (23), Article 235101
• Main Authors: Kaltenborn, Steffen, Zhu, Yao-Hui, Schneider, Hans Christian
• Format: Article
• Language: English
• Subjects: Diffusion; Dynamics; Excitation; Mathematical analysis; Mathematical models; Relaxation time; Signatures; Transport
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.85.235101

Spin and charge-current dynamics after ultrafast spin-polarized excitation in a normal metal are studied theoretically using macroscopic wave-diffusion equations for spin-resolved carrier and current densities. It is shown analytically how this set of equations yields a unified description of ballistic and diffusive properties of spin and charge transport, including the intermediate regime between these two limits. In the framework of the wave-diffusion approach, ultrafast excitation of spin-polarized carriers in thin gold films is modeled assuming slightly spin-dependent momentum relaxation times along with standard parameters (Fermi velocity, spin and momentum relaxation times). The unified treatment of diffusive and ballistic transport yields robust signatures in the spin and charge dynamics that are in qualitative agreement with recent experimental results [Melnikov et al., Phys. Rev. Lett. 107, 076601 (2011) (http://dx.doi.org/10.1103/PhysRevLett.107.076601)]. The influence of boundary effects on the temporal signatures of spin transport is also studied.