  We consider a scanning tunneling microscope (STM) such that tunneling occurs
through two atomically sharp protrusions on its tip. When the two protrusions
are separated by at least several atomic spacings, the differential conductance
of this STM depends on the electronic transport in the sample between the
protrusions. Furthermore two-protrusion tips commonly occur during STM tip
preparation. We explore possible applications to probing dynamical impurity
potentials on a metallic surface and local transport in an anisotropic
superconductor.
