Detecting Crossed Andreev Reflection by Cross-Current Correlations

We consider a hybrid system consisting of two normal metal leads connected to a superconductor through a tunnel barrier. We study current-current correlations of the normal leads at subgap voltages and temperatures. Only two processes contribute to the cross-correlation: the crossed Andreev reflection (emission of electrons in different leads) and the elastic cotunneling. Both processes are possible due to the finite size of the Cooper pair. Noise measurements can thus be used to probe directly the superconducting wave function without the drawbacks appearing in average current measurements where the current is dominated by direct Andreev reflection processes.