Thermoelectric detection of Andreev states in unconventional superconductors

Abstract

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.

18 pages, 7 figures. Updated references, typos corrected

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Cited by in corpus (9)

• Nonlocal quantum heat engines made of hybrid superconducting devices
• Phase-tunable electron transport assisted by odd-frequency Cooper pairs in topological Josephson junctions
• Controllable odd-frequency Cooper pairs in multi-superconductor Josephson junctions
• Thermopower and thermophase in a $d$-wave superconductor
• Identifying Bogoliubov Fermi surfaces via thermoelectric response in a $d$-wave superconductor heterostructure
• Observation of magnetic state dependent thermoelectricity in superconducting spin valves
• Thermoelectric processes of quantum normal-superconductor interfaces
• Complete magnetic control over the superconducting thermoelectric effect
• Phase-dependent charge and heat current in thermally biased short Josephson junctions formed at helical edge states