Insulating State of a Quasi-1-Dimensional Superconductor
The topic of quantum fluctuations in quasi-1D superconductors, also called quantum phase slips (QPS), has
attracted a significant attention. It has been shown that the phenomenon is capable to suppress zero resistivity of
ultra-narrow superconducting nanowires at low temperatures T<<Tc and quench persistent currents in tiny
nanorings. It has been predicted that a superconducting nanowire in the regime of QPS is dual to a Josephson
junction. In particular case of an extremely narrow superconducting nanowire embedded in high-impedance
environment the duality leads to an intuitively controversial result: the superconductor enters an insulating state.
Here we experimentally demonstrate that the I-V characteristic of such a wire indeed shows Coulomb blockade,
which disappears with application of critical magnetic field and/or above the critical temperature proving that the
effect is related to superconductivity. The system can be considered as the dynamic equivalent of a chain of
conventional Josephson junctions.