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Dr. William Meier, February 3rd

“A Catastrophic Charge Density Wave in BaFe2Al9


Charge density waves (CDW) are modulations of the electron density and the atomic lattice that develop in some crystalline materials at low temperature. We identified an unusual example of a CDW in BaFe2Al9 below 100 K based on its low temperature properties. In contrast to the usual CDW phase transition, temperature dependent physical properties of single crystals reveal a first-order phase transition with discontinuous changes in the size of the crystal lattice. In fact, this large strain has catastrophic consequences for the crystals, causing them to physically shatter. Single crystal x-ray diffraction reveals super-lattice peaks in the low-temperature phase signaling the development of a CDW lattice modulation. No similar low-temperature transitions are observed in its sister compound BaCo2Al9. Electronic structure calculations provide one hint to the different behavior of these two compounds; the d-orbital states in the Fe compound are not completely filled. The CDW transition in BaFe2Al9 is unusual in two respects. First, iron materials are renowned for their magnetism and partly filled d-orbitals are key to this. Why does a lattice modulation develop instead of magnetic order? Second, why does this CDW transition occurs with such a destructively large lattice change?


I am condensed matter physicist and material scientist with experience in single crystal synthesis. I completed my bachelor’s degree in ceramic engineering from Missouri University of Science and Technology in 2013. During my PhD work at Iowa State University, I studied condensed matter physics with Paul Canfield. My work focused on synthesis of single crystals of the CaKFe4As4 from high temperature arsenide flux and characterizing this curious 35 K superconductor. After I graduated in 2018, I joined the correlated electron materials group at Oak Ridge National Laboratory. During my time there I continued investigating magnetic intermetallic compounds and I gained experience with neutron scattering, x-ray diffraction and low temperature dilatometry. I joined David Mandrus’ lab at UTK in January 2022 to work on correlated electron materials.