Serhii Volosheniuk1,David Vogel2,Christina Wegeberg2,Marcel Mayor2,3,4,Herre van der Zant1,Pascal Gehring5
Delft University of Technology1,University of Basel2,Karlsruhe Institute of Technology (KIT)3,Sun Yat-Sen University (SYSU)4,Université Catholique de Louvain5
Serhii Volosheniuk1,David Vogel2,Christina Wegeberg2,Marcel Mayor2,3,4,Herre van der Zant1,Pascal Gehring5
Delft University of Technology1,University of Basel2,Karlsruhe Institute of Technology (KIT)3,Sun Yat-Sen University (SYSU)4,Université Catholique de Louvain5
The interaction between magnetic impurities and superconductors leads to fascinating physical phenomena resulting from the competition between Kondo screening and Cooper pair formation [1]. To this end, individual magnetic impurities can form states within the superconducting gap, called Yu-Shiba-Rusinov (YSR) states [1,2]. YSR states are of great interest because they have the potential to realise topological superconductivity. Here we show that such YSR states form in a neutral and stable all-organic radical molecule coupled to proximity induced superconducting break-junction electrodes. We experimentally study the thermoelectric response [3] of the system at mK temperatures, both in the YSR regime and – by applying magnetic fields – in the Kondo regime [4]. Ultimately, we observe a two-fold increase of the thermoelectric efficiency which is induced by the YSR states. This study highlights the power of thermocurrent measurements as a new spectroscopic tool to study nanoscale devices, and reveals new strategies for engineering highly efficient thermoelectric energy conversion at cryogenic temperatures.<br/><br/>[1]K. J. Franke et al., Science 332, 940-944 (2011)<br/>[2]J. O. Island et al., Phys. Rev. Lett. 118, 117001 (2017)<br/>[3]P. Gehring et al., Nat. Nanotechnol. 16, 426-430 (2021)<br/>[4]C. Hsu et al., Phys. Rev. Lett. 128, 147701 (2022)