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Physics Colloquium: Divine P. Kumah

September 9 | 4:00 pm - 5:00 pm

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Title: Emergent Phenomena at Transition Metal Oxide Interfaces

Abstract: Transition metal oxides (TMOs) exhibit a wide range of 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 with regards to
the effects 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

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 LaSrMnO 3 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 LaSrCrO 3 spacer layers, we show that ferromagnetic ordering is
restored in LaSrCrO 3 / LaSrMnO 3 / LaSrCrO 3 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.[1][2] Secondly, we demonstrate the realization of a
high mobility two-dimensional conducting interface between a polar anti-ferromagnet, LaCrO 3 (LCO) and
non-polar SrTiO 3 (STO).[3] Here, the parent materials are insulators, however, structural and electronic
interactions at the LCO/STO 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.

[1] Koohfar et. al., npj Quantum Materials 4 (1), 25 (2019)
[2] Koohfar et. al., Physical Review B 101 (6), 064420 (2020)
[3] Al-Tawhid et. al., AIP advances 10 (4), 045132 (2020)
[4] Al-Tawhid et. al. of Vacuum Science & Technology A 37, 021102 (2019)

Host: Department of Physics



September 9

4:00 pm - 5:00 pm
Event Category: