Exploring the Josephson Scanning Tunneling Microscopy: Towards a Phase-Coherent Junction

Josephson scanning tunneling microscopy (JSTM) is performed by using a superconducting tip on a superconducting sample. The resulting Josephson junction (JJ) is usually too small in terms of critical current and capacitance to support phase coherence between the two superconductors. We are pursuing a concept to overcome that limitation by stabilizing the phase in the scanning junction with a larger JJ in a SQUID loop. We employ a home-built dual-tip STM with connected tips to implement the concept. We characterize the individual junctions by measuring standard I(V) and dI/dV curves, as well as V(I) characteristics which are more common to the study of JJs. In the SQUID configuration, a flux bias of the SQUID should lead to a modulation of the critical current, thus proving the concept.