Modulation of superconducting critical temperature in niobium film by using all-solid-state electric-double-layer transistor

An all-solid-state electric-double-layer transistor (EDLT) was fabricated for electrical modulation of the superconducting critical temperature (Tc) of Nb film epitaxially grown on α-Al2O3 (0001) single crystal. In an experiment, Tc was modulated from 8.33 to 8.39 K while the gate voltage (VG) was varied from 2.5 to −2.5 V. The specific difference of Tc for the applied VG was 12 mK/V, which is larger than that of an EDLT composed of ionic liquid. A Tc enhancement of 300 mK was found at the Li4SiO4/Nb film interface and is attributed to an increase in density of states near the Fermi level due to lattice constant modulation. This solid electrolyte gating method should enable development of practical superconducting devices highly compatible with other electronic devices.