New Structures of Quantized Current Plateaus in Semiconductor Turnstile Devices

Abstract

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 π. We report two new results. (1) New fine structures resulting from the quantized level spacing Δ E appear. Then, the quantized current flows through the barriers via several excited states of the system with a fixed number of electrons, as the source drain voltage increases. These structures are smeared out when the temperature k_BT becomes comparable to Δ E. However the quantized plateaus remain. The quantized plateaus are washed out when k_BT becomes comparable to the charging energy e²/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-averaged 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.