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 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 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