  Interference effects on the transport through two localized tunnel junctions
on the surface of a well-grounded sample reveal intrinsic spatial correlations
characteristic of the uncoupled sample. Differential conductances of the
two-junction probe are related to the spatial correlations of both normal and
superconducting samples. For a superconducting sample the gap anisotropy
strongly affects the results. This may serve as a sensitive probe of the order
parameter in high-temperature superconductors.
