Divine Kumah Seminar
This seminar is generously sponsored by PPG.
Transition metal oxides (TMOs) exhibit many physical properties including high-temperature superconductivity, ferroelectricity, ferromagnetism, and metal-insulator transitions. While these physical properties are understood in the bulk forms of these materials, open questions remain regarding the effects of reduced dimensionality and quantum confinement and the effect of electronic, orbital, spin and structural interactions at heterointerfaces. In this talk, a combination of atomic-scale materials synthesis, synchrotron X-ray high-resolution diffraction and spectroscopy, temperature-dependent transport and magnetometry, high-resolution electron microscopy, and first-principles density functional theory are used to elucidate the interplay between structural and electronic degrees of freedom at TMO interfaces.
First, we show that magnetic and orbital degrees of freedom are coupled to structural interactions at the interfaces between atomically-thin TMO films. We demonstrate the stabilization of robust ferromagnetism in sub-nanometer-thick LaSrMnO3 films. We show that polar structural distortions at LSMO interfaces lead to magnetically ‘dead’ ultra-thin layers. By suppressing these polar distortions using iso-valent and iso-structural LaSrCrO3 spacer layers, we show that ferromagnetic ordering is restored in LaSrCrO3 / LaSrMnO3 / LaSrCrO3 heterostructures. Additionally, we show that the degeneracy of the transition metal d orbitals can be controlled by epitaxial strain leading to competition between ferromagnetic and antiferromagnetic instabilities. Secondly, we demonstrate the realization of a high mobility two-dimensional conducting interface between a polar anti-ferromagnet, LaCrO3 (LCO) and non-polar SrTiO3 (STO) and LaMnO3 and KTaO3. Here, the parent materials are insulators, however, structural and electronic interactions at the oxide interface lead to the formation of an electron gas confined to the interface.
These results demonstrate the strong correlation between the atomic-scale structural properties of 2D materials and their electronic and magnetic ground states with important implications for discovering and understanding quantum materials.
Dr. Divine Kumah's Biography
Divine Kumah is an Associate Professor in the Department of Physics at Duke University. He received his B.S in Physics from Southern University, Baton Rouge, and a Ph.D in Applied Physics from the University of Michigan in 2009. His postdoctoral research work was performed at the Center for Research in Interface and Surface Phenomena at Yale University. Prior to joining Duke in 2023, he was an Associate Professor in the Physics department at North Carolina State University. His research interests are in experimental condensed matter physics and aim to understand the novel electronic and magnetic properties that emerge at the interfaces between crystalline materials. He has received several awards including the National Science Foundation Career Award and the 2022 Oxide Electronics Prize for Excellency in Research.
