The Spin Seebeck effect has first been observed in a transverse
set up. Here, a spin voltage is generated in response to an applied
temperature gradient in a transverse direction. Difficulties in
reproducing these initial findings have lead to a controversy
about the existence or non-existence of this effect.
In order to help clarify this controversy, we calculate the
wavevector-dependent transport of coupled magnons and phonons
in insulating ferromagnets on the basis of a Boltzmann
approach. We find that quasiballistic magnons can indeed contribute
to a finite transverse Spin Seebeck signal. However, this
contribution is tiny at room temperature and might be
observable only at low temperatures.
(F.B. Wilken and T.S. Nunner "Quasiballistic contribution to the
transverse spin Seebeck effect" (in preparation)).