Anisotropic Superconducting Diode Effect in Planar Josephson Junctions

We theoretically investigate the magnetic and crystalline anisotropies of the superconducting diode effect (SDE) in proximitized planar Josephson junctions (JJs) with coexisting Rashba and Dresselhaus spin-orbit couplings (SOCs) under an in-plane magnetic field. A symmetry analysis identifies geometric constraints on magnetic-field and crystallographic orientations for which the SDE is suppressed independently of field strength, providing experimentally testable signatures of the interplay between SOC and Zeeman interaction. We develop a phenomenological model showing that the diode efficiency depends on the relative alignment between spin-orbit and magnetic fields, and corroborate this behavior in the narrow-junction, low-field regime using an analytical approach that links the anisotropy of the diode response to SOC-induced Fermi surface distortions and anisotropic Cooper pair momentum. These findings are supported by tight-binding simulations of the Bogoliubov-de Gennes equation, which reproduce recent experimental trends. The simulations reveal that electrostatic gating can induce polarity reversals of the SDE in the low-field regime even with only Rashba SOC, consistent with recent experiments, and predict additional reversals for specific field orientations, junction geometries, and SOC ratios. Our results elucidate the origin of anisotropic nonreciprocal superconducting transport and provide guidance for experimentally probing the mechanisms underlying the SDE in semiconductor-based planar JJs.