Thermoelectric signatures of order-parameter symmetries in iron-based superconducting tunnel junctions

Thermoelectrical properties are frequently used to characterize materials and endow the free energy from wasted heat with useful purposes. Here, we show that linear thermoelectric effects in tunnel junctions with Fe-based superconductors not only address the dominance between particle and hole states but also even provide information about the superconducting order-parameter symmetry. In particular, we observe that nodal order parameters present a maximal thermoelectric effect at lower temperatures than for nodeless cases. Furthermore, we show also that superconducting tunnel junctions between Fe-based and BCS superconductors could provide a thermoelectric efficiency ZT exceeding 6 with a linear Seebeck coefficient around S≈800 µV/K at a few kelvins. These results pave the way to developing novel thermoelectric machines based on multiband superconductors.