  The atomic variations of electronic wavefunctions at the surface and electron
scattering near a defect have been detected unprecedentedly by tracing
thermoelectric voltages given a temperature bias [Cho et al., Nature Mater. 12,
913 (2013)]. Because thermoelectricity, or Seebeck effect, is associated with
heat-induced electron diffusion, how the thermoelectric signal is related to
the atomic-scale wavefunctions and what the role of the temperature is at such
a length scale remain very unclear. Here we show that coherent electron and
heat transport through a point-like contact produces an atomic Seebeck effect,
which is described by mesoscopic Seebeck coefficient multiplied with an
effective temperature drop at the interface. The mesoscopic Seebeck coefficient
is approximately proportional to the logarithmic energy derivative of local
density of states at the Fermi energy. We deduced that the effective
temperature drop at the tip-sample junction could vary at a sub-angstrom scale
depending on atom-to-atom interaction at the interface. A computer-based
simulation method of thermoelectric images is proposed, and a point defect in
graphene was identified by comparing experiment and the simulation of
thermoelectric imaging.
