Efficient superconducting diodes in three-dimensional vortex landscapes

Non-reciprocal transport has recently regained significant interest of the community, called "superconducting diode". The requirements of simultaneous broken time-reversal and inversion symmetries are readily achieved in conventional superconductors in weak magnetic fields. Exceptional control over vortex barrier anisotropies had been demonstrated in patterned thin-films and heterostructures. Here we present a novel approach to the problem by controlling the cross-sectional shape of micron-sized superconducting bars in truly three-dimensional conductors. In particular, equilateral triangular cross-sections allow the magnetic field direction to continuously tune the degree of mirror-symmetry-breaking, interpolating between reciprocal transport for fields along the mirror planes of the triangle and maximally non-reciprocal situations when fields are between two mirror planes. Experimentally, we utilize focused ion beam direct-write methods to deposit these triangular superconducting bars from WCO precursors, providing a robust superconductor with very high vortex mobility. Accordingly, strong diode behavior is observed at low currents (<1mA) and low magnetic fields (<20mT). These experiments point to an underexplored direction of vortex landscape design by controlling the 3D cross-section of micron-sized superconducting structures.