Kondo Model for the “0.7 Anomaly” in Transport through a Quantum Point Contact

Experiments on quantum point contacts have highlighted an anomalous conductance plateau around $0.7(2e^2/h)$, with features suggestive of the Kondo effect. Here, an Anderson model for transport through a point contact analyzed in the Kondo limit. Hybridization to the band increases abruptly with energy but decreases with valence, so that the background conductance and the Kondo temperature $T_K$ are dominated by different valence transitions. This accounts for the high residual conductance above $T_K$. The model explains the observed gate-voltage, temperature, magnetic field, and bias-voltage dependences. A spin-polarized current is predicted even for low magnetic fields.