Dissipative Cooper Pair Tunneling at the Atomic Scale

In scanning tunneling microscopy (STM) tunneling is dominated by sequential charge transfer. In particular, due to the atomic size junction at temperatures below about 1K the charging energy of the junction capacitance is typically the dominant energy scale, larger than the Josephson energy and much larger than the thermal energy. The granularity of the tunneling current through charge quantization becomes measurable manifesting itself as the dynamical Coulomb blockade (DCB). Due to the concomitant strong phase fluctuations, Cooper pairs cannot tunnel dissipationless anymore and energy has to be exchanged with the local electromagnetic environment, which turns the DCB into an anti-blockade actually enabling Josephson tunneling. We show how enhancing the energy resolution in the STM enhances the range of electromagnetic modes that can be probed with Cooper pair tunneling up to wavelengths in the centimeter range. In this way, microscopic tunneling can be influenced on a macroscopic scale.