Magnetic Splitting of the Zero Bias Peak in a Quantum Point Contact with a Variable Aspect Ratio

We have measured the nonlinear conductance of a four-gate Quantum Point Contact (QPC) device fabricated in a GaAs/AlGaAs heterostructure containing a 2-dimensional electron gas. By continuously varying the longitudinal potential profile of the QPC, we controllably create and destroy a local bound state. The nonlinear transport data show both a characteristic Coulomb blockade diamand and a zero-bias peak similar to the Kondo effect signature peak in quantum dots. We find that even when the bound state is suppressed the zero-bias peak persists. Applying an in-plane magnetic field perpendicular to the direction of the current produces a splitting of the peak which closely matches the $g$-factor data obtained via the cotunneling spectroscopy method in a separate quantum dot on the same chip.