Figure 1

(a) Scanning electron microscope image of the device. Each of the two normal islands (colored red or green) is inserted between two sets of superconducting junctions. One junction pair is used as a cooler (or heater), and the other one is used as thermometer. (b) Schematic side view of the setup. The top (t) and bottom (b) levels are galvanically isolated from each other by a 40-nm-thick layer of Si. (c) Heat transfer model. Electrons and phonons of the bottom (top) island at the respective temperatures $T_{e,b}$ and $T_{\mathrm{ph},b}$ ($T_{e,t}$ and $T_{\mathrm{ph},t}$) exchange a heat power ${\dot{Q}}_{e-\mathrm{ph}}^b$ (${\dot{Q}}_{e-\mathrm{ph}}^t$). Phonons of each island are coupled together via the Kapitza power ${\dot{K}}_{b-t}$ and to the bath phonons via ${\dot{K}}_{b-s}$ and ${\dot{K}}_{t-s}$.Reuse & Permissions

Figure 2

(a) Electronic temperatures $T_{e,b}$ and $T_{e,t}=T_{\mathrm{ph},t}$ as a function of the voltage $V$ across the bottom cooler/heater junctions at a bath temperature $T_{\mathrm{bath}}=432$ mK. (b) Temperature variations $\mathrm{<ruby><rb>\Delta </rb><rt>でるた</rt></ruby>}{T}_{e,b}$ and $\mathrm{<ruby><rb>\Delta </rb><rt>でるた</rt></ruby>}{T}_{e,t}=\mathrm{<ruby><rb>\Delta </rb><rt>でるた</rt></ruby>}{T}_{\mathrm{ph},t}$ based on the same data, with the latter temperature change being amplified by a factor of 30. (c) Maximum of $\mathrm{<ruby><rb>\Delta </rb><rt>でるた</rt></ruby>}{T}_{e,b}$ (circles) and $\mathrm{<ruby><rb>\Delta </rb><rt>でるた</rt></ruby>}{T}_{e,t}$ (squares) as a function of the bath temperature.Reuse & Permissions

Figure 3

Electronic temperatures $T_{e,b}$ (green circles) and $T_{e,t}$ (red diamonds) as a function of the absolute value of the power injected (a) in the bottom island or (b) in the top island. Gray squares in (a) show $T_{e,b}$ plotted as a function of the raw power ${\dot{Q}}_N^0$, while all other data are plotted as a function of the corrected power ${\dot{Q}}_N={\dot{Q}}_N^0+\mathrm{<ruby><rb>\alpha </rb><rt>あるふぁ</rt></ruby>}{Q}_S$. In (a), the dash-dotted and the dotted lines corresponds to the point where the powers ${\dot{Q}}_N^0$ and ${\dot{Q}}_N$, respectively, change sign. The solid lines are fits calculated using the thermal model discussed in the text and a single set of parameters. The black dotted lines indicate the calculated phonon temperature of the island that is cooled or heated. Bath temperature is 281 mK for (a) and 432 mK for (b). Insets depict the relevant experimental schemes.Reuse & Permissions