Large capacitance in the nanosecond-scale transient response of quantum point contacts

Abstract

The transient electrical response of split-gate quantum point contacts (QPCs) is investigated using ultrashort voltage pulses with rise times as small as 2ns. Our measurements reveal a large (∼1nF) parallel capacitance under conditions where the QPC is formed. The capacitance is independent of the QPC gate geometry, and the amplitude and rise time of the applied transient pulse. Some speculations on the source of this capacitance are offered.