A fundamental question in condensed matter physics has just been elucidated by researchers at IPCMS : How fast does it take to the orbital angular momentum of the electron to couple to its spin momentum ?
This interrogation has been raised by the Strasbourg group more than 10 years ago after their pioneering work in femtomagnetism* . The researchers, which results have just been published in the journal Nature , have demonstrated that this time is of the order of 60 fs (1fs = 10-15s).
This result is very important for the ultrafast storage of information since it gives a minimum value for addressing a magnetic medium using low intensity laser pulses. The experiments allowing to observe the dynamics of this spin-orbit coupling have been performed with Cobalt-Palladium ferromagnetic films. They consisted in measuring separately the projections of the orbital angular moment Lz and spin Sz in the direction perpendicular to the plane of the film. To achieve that, time resolved XMCD magnetic circular dichroism measurements have been made using femtosecond Xrays on the femtoslicing beam line of the BESSY synchrotron source in Berlin operated by a German team.
* modification of magnetization using femtosecond laser pulses
 Nature 465, 468 (2010) Distinguishing the ultrafast dynamics of spin and orbital moments in solids; C. Boeglin, E. Beaurepaire, V. Halté, V. Lopez-Flores, C. Stamm, N. Pontius, H. A. Dürr & J.-Y. Bigot.
Dynamics of the orbital and spin angular moments in CoPd ferromagnetic films.