Transport characteristics of series ballistic point contacts

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