1.4 Spin-orbit Coupling in Solid Materials

Eq. (1.59)tells us that the spin-orbit coupling effect is proportional to the inverse of double Einstein energy 2mc2≈1MeV. So this effect is usually weak unless the potential gradient is sufficiently large. You may wonder whether one can create an artificial material or structure so that the po-tential gradient becomes rather large, and then one can have a system with significant strength of spin-orbit coupling.