  In this work, we explore the generalities of the supercurrent diode effect.
As an illustrative example, we examine a model of a two-dimensional
superconductor with Rashba-type spin-orbit coupling under an in-plane magnetic
field and in the clean limit, which realizes a helical phase. First, we utilize
Ginzburg-Landau phenomenology to derive a general formula for the diode
efficiency. This is achieved by incorporating higher gradient terms in the
Lifshitz invariants, which are responsible for the nonreciprocal superflow.
Subsequently, we validate these results through microscopic diagrammatic
computation and further estimate correction terms arising from interband
pairing correlations. We provide a detailed comparison to prior investigations
of this problem conducted within the framework of the quasiclassical
approximation based on the Eilenberger equation.
