Electronic and Magnetic Excitations in Correlated and Topological Materials

Modern condensed matter physics often deals with materials that display strong electronic correlations, such as high-temperature superconductors or heavy fermion compounds. The present work examines the heavy fermion material CeCoIn5, starting with the extraction of its low-energy electronic structure from cutting-edge scanning tunneling spectroscopy experiments by the Davis group (Cornell U.). This information, along with the assumption that the magnetic interaction between f-electrons provides the superconducting pairing, leads to a series of predictions about the superconducting state of CeCoIn5 that are in good agreement with experiment. Nonequilibrium transport experiments can also provide important insight into the properties of materials. Calculations of the current flow in nanoscale heavy fermion compounds are performed which reveal the important roles played by defects and hybridization correlations. The suppression of the latter in the presence of finite bias is also addressed. Finally, transport in nanoscale 2D topological insulators is studied in a similar framework. It is shown how, by placing magnetic defects at the edge of the sample, highly spin-polarized currents may be generated, leading to tunable spin diodes. These effects are robust against various perturbations and have potential application in the growing fields of spintronics and quantum computation.