Ultra-fast dynamics in solids: Non-equilibrium behaviour of magnetism and atomic structure

Abstract

Non-equilibrium physics is of fundamental interest, for example, for extensions of statistical mechanics and thermodynamics. In particular, it is important to understand how conservation laws like energy conservation and angular-momenturn conservation in magnetic solids control the time scale of the dynamics. Laser irradiation may cause intense electronic excitations and thus a strong non-equilibrium state. Results are presented for the ultra-fast response of magnetism in ferromagnetic transition metals like Ni, Co, Fe, and Gd and furthermore of the atomic structure in semiconductors like Si, Ge, and InSb. Non-thermal melting is a most spectacular example of ultra-fast bond breaking. Time-resolved magnetooptical experiments yielding sub-picosecond spin dynamics are discussed. The spin dynamics is accompanied by THz light emission. The structural changes in semiconductors, bond changes sp3 → s 2p2, and phase transitions occur within about 100 fs. The results also shed light on electron-transfer processes, on ionization, and on molecular dissociation dynamics, which may occur during fs and as times. We discuss the application of time-resolved analysis to tunnelling problems and the phase diagram of high-TC superconductivity. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.