A recently published paper in Nature Physics by a research group led by Jeremy Levy, distinguished professor of condensed matter physics at the University of Pittsburgh and founding director of the Pittsburgh Quantum Institute, describes how the Kronig-Penney model is reproduced within a programmable oxide material.
The Kronig-Penney model, introduced in 1931 by Ralph Kronig and William Penney, shaped the understanding of semiconductors, metals and insulators—the materials that are used to create computers and many other technologies.
The lead author, Megan Briggeman, used an atomic force microscope in a manner they describe as analogous to an Etch-A-Sketch toy, and created an artificial one-dimensional lattice of buckets for electrons that repeats every 10 nanometers. In real materials, the buckets are formed from individual atoms spaced from one another by a fraction of a nanometer.
Briggeman found that electrons placed into this artificial lattice interact in unexpected ways, and in some sense behave as though the charge carriers were fractions of an electron. The experimentally observed behavior, partly explained by theory, extends far beyond the simple model of Kronig and Penney. In contrast to the Kronig-Penney model, the real system contains hundreds of electrons, which interact in complex ways that give rise to the observed behavior.
The research is part of a larger effort to produce, through quantum simulation, new electronic states of matter which could be helpful in developing future quantum technologies like quantum computers.
Other researchers involved in the research are Hyungwoo Lee, Jung-Woo Lee and Ki-Tae Eom at the University of Wisconsin-Madison, François Damanet, Elliott Mansfield, and Andrew Daley at the University of Strathclyde, and Jianan Li, Mengchen Huang, and Patrick Irvin at the University of Pittsburgh. The research was supported by the Office of Naval Research, National Science Foundation, Department of Energy, Air Force of Office of Scientific Research and the Engineering and Physical Sciences Research Council (UK).