Ultra‐fast dynamics in solids: non‐equilibrium behaviour of magnetism and atomic structure

Abstract

AbstractNon‐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‐momentum 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 → s2p2, 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.