All-optical spin switching: A new frontier in femtomagnetism -- A short review and a simple theory

摘要: Using an ultrafast laser pulse to manipulate the spin degree of freedom has broad technological appeal. It allows one control dynamics on a femtosecond time scale. The discipline, commonly called femtomagnetism, started with pioneering experiment by Beaurepaire and coworkers in 1996, who showed subpicosecond demagnetization occurs magnetic Ni thin films. This finding motivated extensive research worldwide. All-optical helicity-dependent switching (AOS) represents new frontier where single can permanently switch without any assistance from field. review summarizes some crucial aspects this discipline: key experimental findings, leading mechanisms, controversial issues, possible future directions. emphasis is our latest investigation. We first develop all-optical rule that determines how switchability depends light helicity. understand microscopically reversed why circularly polarized appears more powerful than linearly light. Then we invoke spin-orbit coupled harmonic oscillator model simulate reversal. consider both cw excitation pulsed excitation. results are good agreement result. then extend code include exchange interaction among different sites. show "inverse Faraday field" comes affects reversal nonlinearly. Our hope will motivate theoretical investigations discussions.