Strongly asymmetric single-electron transistor operating as zero-biased electrometer

We have studied a strongly asymmetric Al single-electron transistor with $R_1\ll R_2$ and $C_1\gg C_2$, where $R_{1,2}$ and $C_{1,2}$ are the tunnel resistances and capacitances of the first and second junction respectively. Due to asymmetry in its electric parameters, leading to strong asymmetry of the nonlinear $I$-$V$ curve at zero bias $(V=0)$, the transistor demonstrated remarkable current response to ac signal at the values of gate charge $Q_0$ close to $(n+1/2)e$, where $n$ is integer. A rather delicate regime of the transistor operation ($V\ll e/C_\Sigma$) being important for unperturbed measurements was examined. The measured curves are in good agreement with a model based on the orthodox theory of single electron tunneling. This specific zero bias regime of asymmetric transistor opens new opportunities for single-electron transistor as ultra-sensitive charge/field sensor.