Field Effect Control of <inline-formula> <tex-math notation="TeX">$T_{\rm c}$</tex-math></inline-formula> in Y-Ba-Cu-O Electric Double Layer Transistors

Abstract

Electric-double-layer field-effect-transistors (EDLFETs) were fabricated using 10.5-12.9 nm thick YBa 2 Cu 3 O 7 (YBCO) films and N, N-Diethyl-Nmethyl-N-(2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide (DEME-TFSI), and critical temperature (T c ) and vortex behavior were evaluated in the devices. Decrease in sheet resistance and increase in Tc were observed when negative gate voltage (V G ) was applied, and opposite variation was observed in the case of positive gate voltage. At V G = 0 V, T c onset was ~70 K, and T c0 was ~47 K. V G = -5 V resulted in T c onset of 83.3 K and T c0 of 61.8 K, and those in V G = +2 V were 65.0 K and 40.0 K. To discuss carrier doping mechanism, activation energy for vortex motion and irreversibility temperature were measured at V G = 0 V and -3 V. Activation energy and irreversibility temperature were improved by negative gate voltage. This shows that carrier doping was performed throughout thickness of film since vortices moved with length scale larger than coherence length. This suggests that electrochemical reaction such as oxygen ion injection strongly affected carrier density in the present devices.