The remarkable physics of two-dimensional (2D) electronic systems has led to 3 sets of Nobel Prizes (1985, 1998, and 2010) and radically changed our understanding of electrons in materials. Experimenters most often probe these systems using electrical transport measurements involving passing an electrical current through the 2D electronic system and measuring voltages appearing across the sample. Such measurements have revealed amazing behaviors such as the quantum Hall effects and the existence of "edge-states" with quantized conductance. However, these and many other measurements have a main limitation in what they tell us about the system: they only have sensitivity to the behavior of electrons near the Fermi energy. Quantum mechanical tunneling, in contrast, can probe electronic states away from the Fermi level. This talk will introduce a contactless tunneling method that utilizes millions of short electrical pulses to induce tunneling currents into and out of 2D electronic systems and yields precise tunneling spectra of 2D system even in regimes where it is electrically insulating. The measurements have revealed remarkable new physics such as: (1) a sharp resonance in tunneling that arises from vibrations of 2D electrons in a "Wigner Crystal"; (2) structure appearing in tunneling spectra that give a direct measurement of the short-range interactions between electrons; (3) measurement and visualization of the 2D energy levels as a function of momentum; (4) observation of polarons and a novel phonon analog of the vacuum Rabi splitting; and (5) measurement of the unusual spin-polarization of the 2D electronic system in magnetic field.
Wtr. Qtr. Colloq. committee: A. Linde (Chair), S. Kivelson, B. Lev, S. Zhang
Location: Hewlett Teaching Center, Rm. 201