Observation of absolute negative resistance in mesoscopic samples of a-NbGe

Local and nonlocal measurements on mesoscopic samples of amorphous NbGe, a high-κ type-II superconductor with very low pinning, reveal peculiar features in close vicinity of the transition temperature Tc: in absence of magnetic field, both local and nonlocal DC voltage current characteristics clearly display absolute negative resistance in a small interval around zero current and a small temperature range immediately below Tc. At the same time, a negative voltage is also observed in both local and nonlocal measurements of R(T). The temperatures at which this occurs are consistently found to be around 0.95-0.96 Tc, which is clearly below the narrow superconducting transition region. Upon application of small external magnetic fields on the order of B=50 mT, the effect can be suppressed. The origin of these completely unexpected features is not clear.