  The superconducting diode effect (SDE) refers to the non-reciprocal nature of
the critical current (maximum current that a superconductor can withstand
before turning into a normal metal) of a superconducting device. Here, we
investigate SDE in helical superconductors with broken inversion and
time-reversal symmetry, focusing on a prototypical Rashba nanowire device
proximitized by an s-wave superconductor and subjected to external magnetic
fields. Using a self-consistent Bogoliubov-de Gennes mean-field formalism, we
analyze the interplay between linear and higher-order spin-orbit coupling
(SOC), bulk supercurrents, and external magnetic fields. Our results
demonstrate that Rashba nanowires with only linear SOC can achieve incredibly
large diode efficiencies > 45% through the interplay of longitudinal and
transverse magnetic fields. Notably, higher-order SOC introduces qualitatively
different behavior, enabling finite diode efficiency even in the absence of a
longitudinal Zeeman field due to inherent energy dispersion asymmetry. We
present a comprehensive phase diagram of the device elucidating the emergent
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state and demonstrate
that proximitized Rashba nanowires offer a versatile, practical platform for
SDE, with potential realizations in existing material systems. These results
provide crucial insights for optimizing SDE in nanoscale superconducting
devices, paving the way for next-generation dissipationless quantum
electronics.
