Electrons in solids form complex quantum phases that challenge our understanding of phenomena in the quantum limit. The ability to tune the electronic wavefunctions through various methods of material fabrication (solid state chemistry or nanofabrication) makes electronic behavior of materials one of the most exciting fields of science. Among the areas at the forefront of electronic materials are phenomena that involve the collective behavior of electrons, such as superconductivity. As demonstrated by our current incomplete understanding of superconductivity in compounds with d and f electrons (some at very high temperatures), the behavior of electrons in exotic materials poses real challenges to our ability to predict collective quantum behavior.
By tuning material properties it is possible to realize new quantum states of matter. For example, recently insulators with strong spin-orbit interaction (involving heavy elements) have been shown to have highly conducting electrons at their surfaces that behave like mass-less (light-like) particles. This unusual state of matter is related to the quantum hall state for electrons in high magnet fields, but realized because of strong interaction between electrons’ spin and orbital degree of freedom in compounds with heavy elements. Finally, the ability to control the quantum behavior of single electrons or their spin trapped in an host material can provide a venue to push the frontiers of creating entangled quantum states and quantum measurements. These electronic phenomena are not only at the frontiers of research in condensed matter physics, but they also provide new opportunities for future technological advances.
Our group’s research approach is to bring the power of local measurements of electronic states with scanning tunneling microscope (STM) to visualize novel quantum states of matter. Microscopes have always played a pivotal role in science by providing new perspectives for understanding how macroscopic behavior emerges from phenomena that occurs on smaller length scales. Our aim is to apply STM techniques, using state-of-the-art instrumentation built in our laboratory, to obtain a precise picture of electronic states in materials with interesting electronic properties. Through these experiments, we strive to understand how an interesting collective property emerges from the behavior of electrons on the nanometer scale.
For example, recently using these instruments our team has been able to visualize the formation superconducting electron pairs in a high–Tc superconductor with lowering of temperature on the atomic scale. Such measurements have provided evidence that pairing in the high–Tc cuprates can occur in nanoscale regions above the transition temperature. In another study, we have been able to visualize electronic state on the verge of localization and found evidence that electron wavefunctions can behave like fractal object. Browsing our web page, you will see that the STM techniques and advance instrumentation in our group have a wide range of application to problems in physics of electrons in materials. We continue to expand our ability to measure and understand the nature of electronic states in materials with these tools.