Microscopic theory of ultrafast spin linear reversal.

摘要: A recent experiment (Vahaplar et al 2009 Phys. Rev. Lett. 103 117201) showed that a single femtosecond laser can reverse the spin direction without precession, or linear reversal (SLR), but its microscopic theory has been missing. Here we show SLR does not occur naturally. Two generic models, Heisenberg and Hubbard are employed to describe magnetic insulators metals, respectively. We find analytically change is always accompanied by simultaneous excitation of at least two components. The only model prospects for Stoner single-electron band model. However, under influence field, orbital angular momenta excited coupled each other. If circularly polarized light used, then all three components excited, so their spins. commutation relation further reveals if exists, it must involve complicated multiple state excitation.