Superconductivity is a macroscopic phenomenon, however when the grain size of the material is smaller than the coherence length, new effects arise. Of particular interest is the superconducting fluctuations regime (above the critical temperature, T_c), which has been measured extensively in the high T_c cuprates. This has been done using the Nernst effect, which is a highly sensitive tool for the detection of superconducting fluctuations.

Granular superconductors (GSC) have been known for many years, with no explanation for their enhanced superconducting properties: Hc₂, T_c. Also, no proof of the expected strong fluctuation regime in these materials has been found.

Due to similarities in the granular electronic properties of cuprates and GSC, we studied the Nernst effect in GSC. We fabricated a homogeneous thin film of granular Al-Al₂O₃ (T_c=2.9K, ΔT_c<0.05K) and found a Nernst signal up to roughly 5.5K. This result is a proof for the existence of superconducting fluctuations far above T_c. We discuss the dependence of the fluctuation regime on the oxygen concentration in the thin film.