We demonstrate that three conductance features, 0.5 and $0.7G_0$ plateaus and a dip at $0.5G_0$, observed in quantum point contacts (QPCs) can be consistently explained by the Rashba interaction in the nonuniform electric field created by the side gates along the transport direction. A quantity $\gamma$ is defined which depends on the extent of this nonuniformity and the electron density. A short QPC tends to have a small $\gamma$. Only when $\gamma$ is large will the Rashba interaction produce a potential well deep enough to localize the electron. This provides the bound state that forms the Kondo resonance with the tunneling electrons. We propose to compare the medium/long QPC to small/large quantum dots, which are governed by the Kondo physics and the Coulomb blockade, respectively. The relation between 0.7 anomaly and the side-gate voltage, length of QPC, and temperature can all be determined to agree qualitatively with the experiments.

• Received 22 September 2008

DOI:https://doi.org/10.1103/PhysRevB.79.033304