Transport characteristics of series ballistic point contacts

Abstract

A double ballistic point contact (D-BPC) structure, where two point contacts are placed in series with a separation of $L_{\mathrm{sp}}$, is fabricated by focused Ga-ion beam scanning. Conductance characteristics for an $L_{\mathrm{sp}=200\mathrm{}}$ nm sample show multiple peaks in their gate-bias dependences. These peaks probably originate from ballistic transport through zero-dimensional levels. The $L_{\mathrm{sp}=400\mathrm{}}$ and 800 nm samples show step structures similar to those of a single point contact. Although plateau resistance values differ from the quantized values ($R_n$) with a zero magnetic field, it is found that they approach $R_n$ as the magnetic field increases.