Effect of phonon focusing and shear waves on anisotropy of drag thermopower in potassium nanoplates

The study of the influence of phonon focusing on the electron-phonon drag has shown that, at low temperatures, the drag thermopower in rectangular-shaped cross-section monocrystalline potassium nanoplates becomes dependent on the orientation of their wide faces in the[011] temperature gradient direction. For the orientation of the wide faces {001}, it has turned out to be larger than that for the orientation {011}. As the transverse parameters of the nanoplates under conditions of competition between the boundary and bulk phonon relaxation mechanisms are increased, thedrag thermopower anisotropy varies in a non-monotonic manner. At a thickness of D approximately equal to 5.10(-6)cm and a width of W = mu D (mu = 3.3), the effect magnitude first changes from 14% to a maximum of 22% at D approximately equal to 310- 5cm. Then, it monotonically decreases and disappears at D >= 0.1cm. With increasing the nanoplates'width-thickness ratio, the value of the orientation anisotropy is shown to riseup to 37%.