  By exploiting our recently derived exact formula for the Lindhard
polarization function in the presence of Bychkov-Rashba (BR) and Dresselhaus
(D) spin-orbit interaction (SOI), we show that the interplay of different SOI
mechanisms induces highly anisotropic modifications of the static dielectric
function. We find that under certain circumstances the polarization function
exhibits doubly-singular behavior, which leads to an intriguing novel
phenomenon, beating of Friedel oscillations. This effect is a general feature
of systems with BR+D SOI and should be observed in structures with a
sufficiently strong SOI.
