The Search for Novel Superconductivity in Inhomogeneous Materials using Magnetic Field Modulated Microwave Spectroscopy
Most major discoveries of high temperature superconductors have not been predicted by theory. While theory can explain experimental findings and motivate ideas of where do search, it does not reliably predict new superconductors. Instead, the best way to find new superconductors is to synthesize many materials and test them. Measuring inhomogeneous samples speeds up this process, allowing the simultaneous testing of several material phases. However, since potential superconducting phases in such samples could be minute, it is necessary to use magnetic field modulated microwave spectroscopy (MFMMS), which is three orders of magnitude more sensitive than conventional magnetometry techniques. MFMMS is used as a first detection method and superconducting samples can be subsequently studied with other measurement techniques. Using MFMMS, superconductivity was detected inside of two meteorite samples and further characterized as an alloy of lead, indium and tin. This is the first detection of extraterrestrial superconducting samples and is significant due to the possibility that these and similar samples could have been superconducting in their natural environment. In addition, MFMMS was used to study chemically doped Sr2IrO4 powder samples. While the superconducting phase detected is likely a known superconductor, SrIr2, this demonstrates this technique’s advantages over conventional magnetometry, which did not measure a superconducting transition. Finally, this dissertation discusses techniques to analyze non-superconducting phase transitions using magnetic hysteresis loops and magnetoresistance measurements. These techniques allows for a more thorough understanding of these transitions, which increases the ability to use MFMMS to characterize unknown phase transitions in homogeneous and inhomogeneous samples.