  We theoretically describe a thermoelectric effect that is entirely due to
Andreev processes involving the formation of Cooper pairs through the coupling
of electrons and holes. The Andreev thermoelectric effect can occur in
ballistic ferromagnet-superconductor junctions with a dominant superconducting
proximity effect on the ferromagnet, and it is very sensitive to surface states
emerging in unconventional superconductors. We consider hybrid junctions in two
and three dimensions to demonstrate that the thermoelectric current is always
reversed in the presence of low-energy Andreev bound states at the
superconductor surface. A microscopic analysis of the proximity-induced pairing
reveals that the thermoelectric effect only arises if even and odd-frequency
Cooper pairs coexist in mixed singlet and triplet states. Our results are an
example of the richness of emergent phenomena in systems that combine magnetism
and superconductivity, and they open a pathway for exploring exotic surface
states in unconventional superconductors.
