Synthesis of Electronic-Grade Quantum Heterostructures

Modern quantum materials are inherently sensitive to point defects, and require a new synthesis route to produce epitaxial oxide thin films and interfaces clean enough to probe fundamental quantum phenomena. The recent discovery of robust superconductivity at KTaO₃ (111) and KTaO₃ (110) heterointerfaces on KaTaO₃ bulk single crystals offers new insights into the role of incipient ferroelectricity and strong spin-orbit coupling. Electronic grade epitaxial thin film platforms will facilitate investigation and control of the interfacial superconductivity and understanding the fundamental mechanisms of the superconductivity in KTaO₃. The major challenge of research on KTaO₃ system is that it is difficult to grow high-quality KTaO₃ epitaxial thin films due to potassium volatility. Recently, we have developed the hybrid PLD method for electronic grade KTaO₃ thin film growth, which successfully achieves this by taking advantage of the unique capabilities of PLD to instantly evaporate Ta₂O₅ in a controlled manner and evaporation of K₂O to maintain sufficient overpressure of volatile species. We successfully synthesized heteroepitaxial KTaO₃ thin films on 111-oriented KTaO₃ bulk single crystal substrates with a SmScO₃ template by hybrid PLD, followed by a LaAlO₃ overlayer. Electrical transport data show a superconducting transition temperature of ~ 1.35K. We anticipate that the ability to synthesize high-quality epitaxial complex oxides such as KTaO₃ that contain volatile elements will provide a new platform for exploring new physics and technological applications arising from unique characteristics such as large spin-orbit coupling.

This works has been done in collaboration with Jieun Kim, Jungwoo Lee, Muqing Yu, Neil Campbell, Shun-Li Shang, Jinsol Seo, Zhipeng Wang, Sangho Oh, Zi-Kui Liu, Mark S. Rzchowski, Jeremy Levy.