New structures of quantized current plateaus in semiconductor turnstile devices

Quantized current plateaus appear in the I - V characteristics of turnstile devices realized by modulating the tunnel barriers with a radio frequency (rf) signal of frequency f and phase difference pi. We report two new resul ts. (1) New fine structures resulting from the quantized level spacing Delt a E appear. Then, the quantized current flows through the barriers via seve ral excited states of the system with a fixed number of electrons, as the s ource drain voltage increases. These structures are smeared out when the te mperature h-BT becomes comparable to Delta E. However the quantized plateau s remain. The quantized plateaus are washed out when k(B)T becomes comparab le to the charging energy e(2)/C, where C is the capacitance of the dot. (2 ) When the rf frequency f becomes larger than the leakage current J(f = 0)/ e, which is the time-averaged current at the frequency f = 0, the time-aver aged current J(dc) is quantized in the adiabatic regime. On the other hand, when f is smaller than J(f = 0)/e, J(dc) is much larger than the quantized current.