  Spin-orbit interaction in semiconductor structures with broken space
inversion symmetry leads to spin splitting of electron and hole states even in
the absence of magnetic field. We discover that, beyond the Rashba and
Dresselhaus contributions, there is an additional type of the zero-field spin
splitting which is caused by the interplay of the cubic shape of crystal unit
cell and macroscopic structure asymmetry. In quantum wells grown along
low-symmetry crystallographic axes, this type of spin-orbit interaction couples
the out-of-plane component of carrier's spin with the in-plane momentum while
the coupling strength is controlled by structure inversion asymmetry. We carry
out numerical calculations and develop an analytical theory, which demonstrate
that this interaction can dominate $\boldsymbol{k}$-linear spin splitting of
heavy-hole subbands.
