Cool electrons to far below room temperature in certain solids with f orbitals, and they gain mass, acting like much heavier particles. In a new study our group has shown, for the first time, how these heavy electrons emerge from entanglement between conduction and f electrons and probed their... Read more
Helical Dirac fermions on the surface topological insulators are a new class of electronic states that could enable dissipation-free spintronics and robust quantum information processors. Our recent study of the influence of disorder on these states shows that although they are resilient against... Read more
An important clue has been discovered in the mystery of the pseudogap state of the high temperature superconducting cuprates. A basic understanding of cuprates has been lacking because scientists do not understand the state out of which superconductivity develops, the so-called pseudogap state.... Read more
Topological surface states are a class of novel electronic states that are of potential interest in quantum computing or spintronic applications. Unlike conventional two-dimensional electron states, these surface states are expected to be immune to localization and to overcome barriers caused by... Read more
Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases of matter. We use atomic scale imaging and spectroscopy with the scanning tunneling microscope to examine the novel electronic states that emerge from the uranium f states in... Read more
High-temperature cuprate superconductors exhibit extremely local nanoscale phenomena and strong sensitivity to doping. While other experiments have looked at nanoscale interfaces between layers of different dopings, we focus on the interplay between naturally inhomogeneous nanoscale regions. Using... Read more
Electronic states in disordered conductors on the verge of localization are predicted to exhibit critical spatial characteristics indicative of the proximity to a metal‑insulator phase transition. We have used scanning tunneling microscopy to visualize electronic states in... Read more
We have used scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy to visualize the gapless surface states in the three-dimensional topological insulator Bi1‑xSbx, and examine in detail the influence of scattering from disorder caused by random... Read more
We have studied high-temperature superconducting cuprates samplesthroughout the doping-temperature phase diagram. We find that the low energy excitations of these systems havea surprising, universal character at low doping. We have developed a procedure to extract the angular dependence of the... Read more
We investigate the source of the variation of the pairing strength in high‑Tc superconductors. We have developed a new technique that allows us to study the same nanoscale region of the material through a broad range of temperatures. Using this technique, we can probe the... Read more
We take an atom-by-atom look at where pairing gaps form in the cuprate superconductor Bi2Sr2Ca2CuO8+δ. When pairing occurs in a superconductor, a gap forms in the density of states (DOS) that can be probed by STM. In... Read more
A novel technique developed by our group uses a scanning tunneling microscope (STM) to substitute atoms into a semiconductor one atom at a time. This technique has been used to assemble a magnetic semiconductor, manganese-doped gallium arsenide (Ga1‑xMnxAs), atom by... Read more
We performed a scanning tunneling spectrocopy characterization of the electronic correlations in the pseudogap state in a high‑Tc superconductor. Heating a normal superconductor above its critical temperature results in a normal metallic behavior, but heating a high-temperature... Read more
Using a scanning tunneling microscope, we demonstrated that a single copper-oxide plane can form a stable layer at the superconductor's surface. This plane behaves differently when exposed at the surface than when buried inside the crystal, offering additional insight into the behavior of... Read more
Scientists recently discovered that nanoscopic peapods — the latest class of nanomaterials created by filling the cores of single‑wall nanotubes — have tunable electronic properties. Our measurements show that encapsulation of molecules can dramatically modify the electronic... Read more
