Absence of diode effect in chiral type-I superconductor NbGe₂

Stemming from the nonreciprocal phenomena in quantum materials, novel functionalities such as superconducting diode effect (SDE) have been achieved in prototype devices through symmetry engineering. Although the SDE is widely observed in various platforms, its underlying mechanism remains debated, particularly regarding the role of vortices. However, it is challenging to rule out the inevitable vortices in type-II superconductors. Here, we systematically investigate the nonreciprocal transport in NbGe₂, a rare material that possesses both chiral structure and type-I superconductivity to circumvent the intricate vortex effect. Moreover, type-II superconductivity with an elevated T_c is induced on the artificial surface by focused ion beam processing, allowing control over vortex dynamics in NbGe₂ devices. We find that the diode efficiency is negligible at low magnetic fields but becomes significant at high magnetic fields, coinciding with an abrupt increase in vortex creep rate when the superconductivity of NbGe₂ bulk is suppressed. This anomalous absence of SDE starkly contrasts with previous observations, where the SDE emerges instantly under external magnetic fields, revealing that the vortex dynamic plays a critical role in SDE besides the well-known symmetry rules.