Cooling electrons from 1 to 0.4 K with V-based nanorefrigerators

The fabrication and operation of V-based superconducting nanorefrigerators is reported. Specifically, electrons in an Al island are cooled, thanks to hot-quasiparticle extraction provided by tunnel-coupled V electrodes. Electronic temperature reduction down to 400 mK starting from 1 K is demonstrated with an estimated cooling power of similar to 20 pW at 1 K for a junction area of 0.3 mu m(2).