Experimental Investigation of Competing Orders, Quantum Criticality and Spin/Charge Transport in Cuprate Superconductors

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This individual investigator award is for an experimental research project that will address some of the most fundamental physics issues associated with high-temperature superconducting cuprates. The primary objectives are: [1] To investigate the competing orders and possible existence of a quantum critical point in different families of hole-doped (p-type) cuprate superconductors as a function of the doping level and temperature by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). [2] To compare the pairing potential, pairing symmetry, and competing orders in the electron-doped (n-type) cuprate superconductors with those in the p-type cuprates. [3] To elucidate the characteristics of spin and charge transport in the p-type cuprate superconductors by studying the effects of spin-polarized and simple quasiparticle injection in perovskite ferromagnet-insulator-superconductor (F-I-S) and in normal metal-insulator-superconductor (N-I-S) heterostructures. The superior spatial resolution of STM/STS is expected to provide unique information for the microscopic properties of cuprate superconductors, and the investigation of spin/charge transport in these superconductors can yield insights into the roles of spin- and charge-degrees of freedom in their pairing state. In addition to the potentially significant impact of these studies on revealing the fundamental physics of cuprate superconductivity, the wide range of forefront experimental techniques employed in conducting this project will provide sound technical and scientific training for the participating students and postdoctoral researchers. Furthermore, novel microelectronic devices based on the tunable superconducting properties of F-I-S heterostructures under variable spin-polarized quasiparticle currents may be devised for a range of applications.%%%This individual investigator award will fund an experimental research project that attempts to address some of the most fundamental physics issues and potential applications associated with high-temperature superconducting cuprates. There are two primary experimental approaches. One involves the use a low-temperature scanning tunneling microscope (STM) to study the microscopic physical properties of cuprates with atomic-scale spatial resolution, thereby proving direct information for the quantum nature of these unconventional superconductors. The other experimental approach involves studying how various superconducting properties of the cuprates are modified under the injection of electrical currents in novel devices comprising of thin-film layers of ferromagnet-insulator-superconductor (F-I-S) and normal metal-insulator-superconductor (N-I-S) heterostructures. In addition to potentially significant impact of these studies on revealing the fundamental physics of cuprate superconductivity, the wide range of frontier experimental techniques employed in conducting this project will provide sound technical and scientific training for the participating students and postdoctoral researchers. Furthermore, the tunable superconducting properties of the F-I-S heterostructures under variable injection currents are promising candidates for various microelectronic device applications.***