Researchers create a one-dimensional lattice for electrons
A study led by Prof. Jeremy Levy of the University of Pittsburgh, with the participation of François Damanet, FNRS research fellow (CESAM/Faculté des Sciences) at ULiège, has led to the creation of a one-dimensional artificial lattice for electrons. These results, published in the journal Nature Physics, represent a breakthrough in the ability to design new families of quantum materials with emerging properties and in the development of one-dimensional quantum simulation platforms in the solid state.
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ur understanding of semiconductor materials, metals and insulators - used in computing to build computers and also present in many other technologies - has been shaped by the Kronig-Penney model. Introduced in 1931 by Ralph Kronig and William Penney, this model provides a simple mathematical approach to determining the energy band structure of quantum particles such as electrons evolving in a periodic potential profile.
A research group led by Jeremy Levy, distinguished professor of condensed matter physics at the University of Pittsburgh (USA) and founding director of the Pittsburgh Quantum Institute, has just described how this Kronig-Penney model can be reproduced in a programmable oxide material. To do this, Megan Briggeman, a physicist at the University of Pittsburgh and first author of the paper just published in Nature Physics, used an atomic force microscope in a way they describe as analogous to a magic screen, and created an artificial one-dimensional lattice of electron buckets that repeats every ten nanometers. In real materials, this bucket structure appears naturally due to the presence of individual atoms spaced a fraction of a nanometer apart.
The study found that electrons placed in this artificial lattice interact in unexpected ways and, in a sense, behave as if the charge carriers were fractions of an electron. The experimentally observed behavior, partially explained by theory, goes far beyond the simple model of Kronig and Penney. "Unlike the Kronig-Penney model, the real system contains hundreds of electrons, which interact in complex ways and give rise to the observed behavior," explains Megan Briggeman. This research is part of a larger effort to produce, through quantum simulation, new electronic states of matter that could be useful in the development of future quantum technologies such as quantum computers.
The Kronig-Penney model is presented in most introductory quantum mechanics and solid state physics courses, but it is somewhat artificial because of its one-dimensional nature. According to Dr. Briggeman, "It was amazing to be able to recreate something that came straight out of the pages of a textbook.”
The published work is the result of a collaboration between different researchers. Hyungwoo Lee, Jung-Woo Lee, Kitae Eom and Chang-Beom Eom of the University of Wisconsin-Madison synthesized the thin films and performed electrical and structural characterizations. From the University of Pittsburgh, Jianan Li and Mengchen Huang processed the samples, and Megan Briggeman, Patrick Irvin and Jeremy Levy conducted the experiments. Finally, François Damanet, Elliott Mansfield and Andrew Daley, from the University of Strathclyde, proposed a theoretical model that could explain some of the experimental observations. François Damanet, who joined the University of Liège during the review process, is now FNRS Research Fellow in the Quantum Optics Unit (CESAM / Faculty of Science) of ULiège.
The research was funded by the Office of Naval Research, the National Science Foundation, the Department of Energy, the Air Force Office of Scientific Research and the Engineering and Physical Sciences Research Council (UK).
Scientific reference
Megan Briggeman, Hyungwoo Lee, Jung-Woo Lee, Kitae Eom, François Damanet, Elliott Mansfield, Jianan Li, Mengchen Huang, Andrew J. Daley, Chang-Beom Eom, Patrick Irvin & Jeremy Levy, One-dimensional Kronig–Penney superlattices at the LaAlO3/SrTiO3 interface, Nature Physics, april 2021
