Single-electron shell occupation and effective g factor in few-electron nanowire quantum dots

Nanowire double quantum dots occupied by an even number of electrons are investigated in the context of energy level structure revealed by electric dipole spin resonance measurements. We use a numerically exact configuration interaction approach up to six electrons for systems tuned to a Pauli spin blockade regime. We point out the differences between the spectra of systems with two and a greater number of electrons. For two electrons the unequal length of the dots results in a different effective g factor in the dots as observed by the recent experiments. For an increased number of electrons the g- factor difference between the dots appears already for symmetric systems and it is greatly amplified when the dots are of unequal length. We find that the energy splitting defining the resonant electric dipole spin frequency can be quite precisely described by the two electrons involved in the Pauli blockade with the lower-energy occupied states forming a frozen core.