Materials Science Research Lecture

Wednesday, October 28, 2020
4:00pm to 5:00pm
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Orbital Degeneracy Lifting: Broken Local Symmetries and their Orderings in Interesting Electronic Materials
Simon Billinge, Professor, Materials Science and Applied Physics and Applied Mathematics, Columbia University, Physicist at Brookhaven National Laboratory,

Webinar Link:

https://caltech.zoom.us/j/95708772987

Webinar ID: 957 0877 2987

Abstract:

Recently, experiments have begun to indicate that broken symmetries that are not long-range ordered but local in nature, and which may be fluctuating, are widespread in transition metals, robust in that they exist over wide ranges of temperature and composition, and have significant impacts on the material properties. They are difficult to detect by conventional measurements sensitive to long-range order, which is why they have been largely overlooked until the past few years, but that doesn't mean that they are not important to the physics of the materials. They can produce gaps in the electronic structure that are large, and in a number of cases studied to date are important, but previously overlooked, precursors to insulator-metal transitions, charge density wave states, nematicity, and more. These broken symmetries are now thought to be electronically driven, removing orbital degeneracies. One example is the well-known Jahn Teller effect, though it is acting locally even in crystalline materials, but other orbital degeneracy breaking mechanisms such as covalency between neighboring metal ions have also been observed, which can result in oligomer formation within solid materials. In this talk I will describe the discovery of this interesting phenomenon we call "Orbital Degeneracy Lifting (ODL)", speculate on how widespread it may be, and some implications for the materials properties.

More about the Speaker:

Prof. Billinge has more than 25 years of experience developing and applying techniques to study local structure in materials using x-ray, neutron and electron diffraction including the development of novel data analysis methods including graph theoretic, Artificial Intelligence and Machine Learning approaches. He earned his Ph.D in Materials Science and Engineering from University of Pennsylvania in 1992. After 13 years as a faculty member at Michigan State University, in 2008 he took up his current position as Professor of Materials Science and Applied Physics and Applied Mathematics at Columbia University and Physicist at Brookhaven National Laboratory. Prof. Billinge has published more than 300 papers in scholarly journals. He is a fellow of the American Physical Society and the Neutron Scattering Society of America, a former Fulbright and Sloan fellow and has earned a number of awards including the 2018 Warren Award of the American Crystallographic Association and being honored in 2011 for contributions to the nation as an immigrant by the Carnegie Corporation of New York, the 2010 J. D. Hanawalt Award of the International Center for Diffraction Data, University Distinguished Faculty award at Michigan State, the Thomas H. Osgood Undergraduate Teaching Award. He is Section Editor of Acta Crystallographica Section A: Advances and Foundations. He regularly chairs and participates in reviews of major facilities and federally funded programs.

For more information, please contact Jennifer Blankenship by email at jennifer@caltech.edu.