Cheng-Rong Xie | Searcharxiv

arXiv2026

Resonant suppression of the $π$-type Josephson component in a Kitaev-ladder junction

We study how discrete normal-segment levels control equilibrium Josephson transport between two Kitaev-ladder superconductors. Away from resonance, detuning opens a selective-clamping window: inter-leg hybridization removes the phase dependence of a $0$-favoring low-energy ground-state contribution while retaining a competing $π$-favoring contribution, allowing a smooth negative first harmonic even for bulk-topologically trivial leads. At resonance and $ϕ=π$, an exact collective-clamping identity makes both low-energy ground-state contributions phase independent above a threshold, although individual quasiparticle levels can remain dispersive. Finite-energy quasiparticles then produce a positive residual first harmonic in a controlled sweet-point regime. For fixed $0<ϕ<π$, helicity mixing instead yields a positive resonant low-energy harmonic in the weak-coupling limit. Exact identities, fourth-order sign rules, and recursive Green-function calculations establish how resonant alignment changes the spectral contributions governing Josephson phase selection.

cond-mat.supr-con↗

arXiv2025

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 $t_\perp$. 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 $ϕ\notin \{0, π\}$ (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 $t_\perp$, 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 $t_\perp$: $η\to 0$ for $t_\perp\to 0$ and for large $t_\perp$, 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.

cond-mat.supr-con↗