Fig. 3: Heat engine characterization.
a Scheme of the circuit used for the heat engine measurement. b Voltage developed across the load (VL) measured at different load resistances (RL) for ∣IH∣ = 40 μA at Tbath = 25 mK and three magnetic field values corresponding to different regimes, i.e., P saturation at 10 mT, remanence at 0 mT, and AP configuration at −10 mT. c Power load (\({P}_{L}=\frac{{V}_{L}^{2}}{{R}_{L}}\)) extracted from panel (b) vs RL. The red curve is a qualitative fit to the 10 mT data from the maximum transferred power law \({P}_{L}=\frac{{R}_{L}{V}_{S}^{2}}{{({R}_{L}+{R}_{S})}^{2}}\), the thermoelectric voltage source VS = Vth ≃ 12.5 μV, and an internal resistance RS ≃ 60 kΩ. d Evolution of PL measured at RL = 150 kΩ and Tbath = 25 mK vs input power (\({P}_{{{{{{{{\rm{in}}}}}}}}}={I}_{H}^{2}{R}_{{{{{{{{\rm{Co}}}}}}}}}\)). e Blow-up of the PL behavior of panel (d). Dash-dotted lines represent the fits to the data considering thermoelectricity with (blue) and without (red) rectification effects. f Efficiency \(\eta=\frac{{P}_{L}}{{P}_{{{{{{{{\rm{in}}}}}}}}}}\), measured as a function of Tbath at RL = 150 kΩ and IH = 40 μA. Full lines are the theoretical prediction for η for different values of h (see Methods section IVB for details), and evaluated for the junction parameters used in the fit of Fig. 1d.
