  We propose a new type of the spin Seebeck effect (SSE) emerging from the
Rashba spin-orbit coupling in asymmetric four-terminal electron systems. This
system generates spin currents or spin voltages along the longitudinal
direction parallel to the temperature gradient in the absence of magnetic
fields. The remarkable result arises from the breaking of reflection symmetry
along the transverse direction. In the meantime, the SSE along the transverse
direction, so-called the spin Nernst effect, with spin currents or spin
voltages perpendicular to the temperature gradient can be simultaneously
realized in our system. We further find that it is possible to use the
temperature differences between four leads to tune the spin Seebeck
coefficients.
