Complex impedance scanning tunneling microscopy: a novel probe to study (un)conventional (super)conductivity

Abstract

The research described in this thesis focuses on the development of a novel microscope to gain a deeper understanding of unconventional superconductors, as a supplement to the scanning tunneling microscope (STM) technique. We combine STM with microwave reflection measurements to locally measure the complex impedance. Hereby we aim to locally probe the resistivity and kinetic inductance in superconductors known to sometimes only exhibit superconductivity locally or inhomogeneously throughout the sample. This technique requires an impedance matching circuit to match the tip-sample impedance to the characteristic impedance of the microwave source. The sensitivity of the microscope to changes in sample impedance is limited by the matching circuit design. The scope of this thesis covers the development of this technique with in-situ replaceable matching circuits and a complementary model to interpret the data, and shows the capabilities of the microscope, which covers local tip-sample impedance measurements with atomic resolution on Au(111) and microwave assisted tunneling experiments on superconducting NbSe2.