Mechanisms for strong anisotropy of in-plane g-factors in hole based quantum point contacts

In-plane hole g-factors measured in quantum point contacts based on p-type heterostructures strongly depend on the orientation of the magnetic field with respect to the electric current. This effect, first reported a decade ago and confirmed in a number of publications, has remained an open problem. In this work, we present systematic experimental studies to disentangle different mechanisms contributing to the effect and develop the theory which describes it successfully. We show that there is a new mechanism for the anisotropy related to the existence of an additional $B_+k_-^4sigma_+$ effective Zeeman interaction for holes, which is kinematically different from the standard single Zeeman term $B_-k_-^2sigma_+$ considered until now.