Josephson diode effect for a Kitaev ladder system

We study the Josephson diode effect realized purely by geometry in a Kitaev-ladder Josephson junction composed of two parallel spinless p-wave chains coupled by an interleg hopping t_⊥. The junction is governed by two phases: the superconducting phase difference across the weak link, $θ$, and the leg-to-leg phase difference, $ϕ$. For ϕ∉ \0, π\ (mod $2π$), time-reversal symmetry is broken, and the absence of leg-exchange symmetry leads to a breakdown of the antisymmetry of the current-phase relation, yielding nonreciprocal Josephson transport without magnetic fields or spin-orbit coupling. By resolving transport into bonding and antibonding channels defined by t_⊥, it is shown that the leg phase acts as an effective phase shift for interband (p_ν/p-ν) tunneling, whereas the same-band (p_ν/p_ν) contribution remains unshifted. These channels arise at different perturbative orders and, together with the $4π$-periodic Majorana channel that emerges near the topological transition, interfere to produce a pronounced diode response. The class-D Pfaffian invariant identifies the parameter regime where the ladder hosts Majorana zero modes. Bogoliubov-de Gennes calculations reveal a dome-like dependence of the diode efficiency $η$ on t_⊥: η→ 0 for t_⊥→ 0 and for large t_⊥, with a maximum at intermediate coupling that is tunable by $ϕ$. The present results establish a field-free, geometry-based route to superconducting rectification in one-dimensional topological systems and specify symmetry and topology conditions for optimizing the effect in ladder and network devices.