When 10:30 AM - 11:30 AM Sep 25, 2015
Where 1571 G.G. Brown
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Internal Charge Transfer at MBE-Grown Complex Oxide Interfaces: New Insights and Opportunities


Bharat Jalan
University of Minnesota, Department of Chemical Engineering and Materials Science

Complex oxide heterostructures can show strong correlation effects, novel magnetism, high breakdown voltage, and high 2D electron density (of the order of 1014 cm-2), unattainable in traditional semiconductor heterostructures. High 2D electron densities are of particular interest for studying low-dimensional physics in narrow d-band materials, in addition to fabricating novel plasmonic field-effect devices (FETs). Recent advances in thin film growth approaches have enabled the growth of this material class in thin film and heterostructure forms with pristine structural quality (similar to that of the conventional semiconductors). However the grand challenge in the field is to obtain these materials with the high level of stoichiometric and defect control.

 

In this talk, I will present my group’s effort to address these challenges and to utilize intrinsic defects as a new degree of freedom to control material’s property using the hybrid molecular beam epitaxy (MBE) approach with the focus on understanding and controlling novel electronic and magnetic ground states in defect-managed oxide thin films and heterostructures. In particular, I will discuss the role of intrinsic defects in realizing the 2D electron gas at perovskite oxide heterojunctions and how 2DEG density identical to that based on polar discontinuity can be achieved using defect-managed structure.

 

I will then present a novel approach for creating high-density 2DEGs at perovskite heterojunction using internal charge transfer. 2D carrier density much higher density than expected based on resolution of the polar discontinuity at perovskite oxide heterojunctions can be achieved via internal charge transfer using band-engineering approaches. Combining DFT modeling and experiments using x-ray photoelectron spectroscopy, scanning transmission electron microscopy, electron energy loss spectroscopy, energy dispersive x-ray spectroscopy and electronic transport measurements, I will discuss the origin of these carriers, dimensionality and transport mechanisms.

 

Finally, I will discuss how electron and hole doping via band-engineered approaches may provide an exceptional route to revisit the phase diagrams of transition metal oxides in the “clean” doping limit.

 

This research is supported through the University of Minnesota MRSEC under awards DMR-0819885 and DMR-1420013.

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