Evidence for the formation of quasibound states in an asymmetrical quantum point contact

Features below the first conductance plateau in ballistic quantum point contacts (QPCs) are often ascribed to electron interaction and spin effects within the single mode limit. In QPCs with a highly asymmetric geometry, we observe sharp resonance peaks when the point contacts are gated to the single mode regime, and surprisingly, under certain gating conditions, a complete destruction of the 2e(2)/h first quantum plateau. The temperature evolution of the resonances suggest non-Fermi-liquid behavior, while the overall nonlinear characterizations reveal features reminiscent of the 0.7 effect. We attribute these unusual behaviors to the formation of a quasibound state, which is stabilized by a momentum mismatch accentuated by asymmetry.