Fig. 1: A molecular heat engine in the YSR regime.
From: Enhancing thermoelectric output in a molecular heat engine utilizing Yu-Shiba-Rusinov bound states
a Sketch of a superconductor-quantum dot-superconductor (S-QD-S) system. An unpaired spin (orange sphere) residing on the QD, in our case a single molecule, couples to a Cooper pair (purple spheres) inside the proximitized gold leads forming YSR bound states. b Energy filtering via YSR states. A thermoelectric current Ith (red arrow) is flowing from the left (hot) side to the right (cold) side. The grey dotted lines depict the Fermi-Dirac distribution functions of the leads. c Schematic of the thermopower device (back gate electrode (pink), heaters (light blue), golden bridge (yellow), superconducting contacts (grey)). The circuit diagram indicates which terminals are used to apply a gate voltage VG, a dc bias voltage VB, an ac bias voltage Vac (ω1) and an ac heater current Ih (ω2), and which terminals are used to measure the dc Idc, the ac Iac (ω1) and the thermocurrent Ith (ω2). The insert shows the structure of the Nitronyl nitroxide diradical molecule (NNDR) which posseses two free spins on the oxygen atoms. d Map of the differential conductance as a function of gate and bias voltage recorded at 62 mK. The bound states and the superconducting gap are highlighted by green and white dotted lines, respectively.
