A Sub-Kelvin Scanning Tunneling Microscope and Its Application to MgB2 and CeCoIn5

A low temperature, high magnetic field, ultra high vacuum scanning tunneling microscope has been constructed. Such an environment places many constraints upon the design of the instrument, but also allows the study of many exotic phenomena, in particular superconductivity. The low temperatures permit high energy resolution, and the high field allows access to novel material phases.

We have leveraged the rare ability to optically access the tunnel junction in order to study materials that are only available in very small sizes. Such samples would be difficult to study in many other low temperature systems.

We have recorded the first superconducting spectroscopy in CeCoIn5 in the <100> direction. CeCoIn5 shows a rich interplay of magnetism and superconductivity. The nodal direction has been confirmed, and evidence for multiband superconductivity is presented.

We have also tunneled into the Meissner rim of MgB2 and observed the effect of a transverse current on the spectroscopy.

The new STM has demonstrated its ability to measure novel materials in difficult configurations at low temperature.