Hosted By: Dr. Julia Zaikina 

Title: Breaking Symmetry to Induce Novel Properties in van der Waals Transition Metal Chalcogenides

Bio: Dr. Efrain E. Rodriguez is Professor of Chemistry and Biochemistry and Materials Science and Engineering at the University of Maryland College Park. He has established a program in solid-state and materials chemistry with a multidisciplinary approach for the preparation and study of functional inorganic materials. He is also a core member of the Maryland Quantum Materials Center. Efrain received his B.S. from the Massachusetts Institute of Technology and his PhD from the University of California, Santa Barbara. At UCSB. After his PhD, Efrain went to the National Institute of Standards and Technology (NIST) for his National Research Council post-doctoral fellowship.  Efrain received the Margaret C. Etter Early Career Award in 2019 from American Crystallographic Association and the CAREER award from the NSF. In 2019, he joined the Board of Directors at the American Institute of Physics. In 2022, he was elected to the US National Committee on Crystallography and the Executive Committee of the Neutron Scattering Society of America. He was awarded the Alexander von Humboldt Fellowship for Experienced Researchers in 2022 to work as a visiting researcher at the Max Planck Institute in Solid State Research in Stuttgart, Germany. In 2023, he was recognized by the University of Maryland as a Distinguished Scholar Teacher.

Abstract: When materials break symmetry, we can observe extraordinary and novel macroscopic properties. In this seminar, I will focus on two categories of materials we design and synthesize: non-centrosymmetric metal chalcogenides as quantum materials and transition metal chalcophosphates as multiferroic systems. In both cases, we work with layered materials with weak van der Waals interactions along the stacking direction. The first category broadly encompasses superconductors and magnetic materials. In this seminar I will cover layered transition metal chalcogenides such as iron selenide (FeSe) and dichalcogenides such as tantalum diselenide (TaSe₂) or niobium diselenide (NbSe₂) intercalated by a variety of species that control the functionality of the quantum material. Our design strategy is to stack metal chalcogenide layers using either molecular complexes or ions to break their inversion symmetry and induce a non-centrosymmetric structure. For the second category of materials, I will discuss our efforts to prepare materials with the composition CuMP₂Q₆ where M = trivalent metal and Q = S or Se to establish multiferroic properties. In these materials, the Cu⁺ cation undergoes an order-disorder transition above room temperature that induces ferroelectricity while the trivalent metal can order in an antiferromagnetic or ferromagnetic fashion. We use powder and single crystal neutron diffraction studies to further elucidate the mechanism for this symmetry breaking.