  We propose theoretically a new effect, i.e. nonlinear planar Nernst effect
(NPNE), in nonmagnetic topological insulator (TI) Bi2Te3 in the presence of an
in-plane magnetic field. We find that the Nernst current scales quadratically
with temperature gradient but linearly with magnetic field and exhibits a
cosine dependence of the orientation of the magnetic field with respect to the
direction of the temperature gradient. The NPNE has a quantum origin arising
from the conversion of a nonlinear transverse spin current to a charge current
due to a joint result of hexagonal warping effect, spin-momentum locking, and
the time-reversal symmetry breaking induced by the magnetic field.
