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.