How spin and orbital angular momenta are correlated during laser-induced ultrafast demagnetization*

It is very well known that there is some degree of correlation

between spin and orbital degrees of freedom during laser-induced

ultrafast demagnetization. What is unknown or less clear is how

they are correlated. The experiments now have accumulated rich

sets of data from different types of materials, from 3d

transition ferromagnets to rare-earth materials.  Here, we use

time-dependent Liouville density functional theory and regular

TDDFT methods to demonstrate clearly that this correlation

exists. Due to spin-orbit coupling, the spin is dragged by the

orbital. In all the six systems that we investigated, we find

this correlation is element-specific. This information is crucial

to understanding demagnetization.  As researchers shift their

views toward phonon-based demagnetization mechanisms, we are

reminded that there are still much more important issues

overlooked so far. If the phonon angular momentum transfer is

important, then it must show up in the spin-orbital correlation

diagram.