Scanning Tunneling Microscopy Studies of the Heavy-fermion Superconductor (100) CeCoIn5 in the Normal Conducting State

Abstract

This thesis reports scanning tunneling microscopy (STM) measurements of the heavy-fermion material CeCoIn5 on the previously unmeasured (100) termination surface. This study demonstrates both the experimental feasibility of measuring these surfaces and the observation of interesting electronic properties. The measurements presented here open the possibility for future experiments to go to lower temperature to explore new aspects of the unconventional superconducting nature of CeCoIn5. In the present work, we study (100) CeCoIn5 in the normal conducting phase. Through topographic and spectroscopic measurements, we demonstrate some of the remarkable physical properties of this material. Topographic maps reveal two surfaces, of which one bears strong resemblance to the bulk crystal structure. Spectroscopic measurements on this surface show both angstrom-scale and nanometer-scale spatial modulation of the electronic density of states. The short wavelength modulation corresponds to the local hybridization of f electrons with the conduction electron sea and also demonstrates the twodimensional character of the material. The long wavelength modulation arises from electronic scattering on the surface, and is shown to prefer certain crystallographic directions, a result that further characterizes the importance of layering in the CeCoIn5 system. The wavelength, energy dependence, and direction of the waves gives indirect information about the Fermi surface. Our measurements show several distinct scattering wavevectors that appear qualitatively consistent with calculated band structure.