Yoshi Krockenberger (NTT Basic Research Laboratories): LRSM Seminar

Title: “Molecular beam epitaxy of functional complex 4d & 5d transition metal oxides”

Yoshi Krockenberger

Distinguished Senior Research Scientist, NTT Basic Research Laboratories, Japan

Dr. Yoshiharu Krockenberger is a distinguished senior research scientist at NTT Basic Research

Laboratories in Japan. He earned his Diploma in Physics from the Technical University of Munich, Germany, where he conducted pioneering electron-tunneling spectroscopy experiments on cuprate superconductors at the renowned Walther-Meissner Institute. During his doctoral studies at the Technical University of Darmstadt, Germany, Dr. Krockenberger delved deeper into the intricacies of superconductivity while concurrently synthesizing novel superconducting materials under the guidance of Professor Bernhard Keimer at the Max Planck Institute for Solid State Research. His exceptional academic achievements culminated in a PhD in Physics summa cum laude in 2006. Following his doctoral studies, Dr. Krockenberger joined the esteemed correlated materials research group of Professor Yoshinori Tokura at RIKEN, Japan. Since 2010, he has been a distinguished senior scientist at NTT Basic Research Laboratories, where he leads groundbreaking research efforts to develop methods and materials for next-generation superconductors. Throughout his illustrious career, Dr. Krockenberger has mentored and supervised numerous talented graduate students and postdoctoral researchers from around the world, fostering a vibrant research community and contributing to the development of future generations of scientists. His research has resulted in over 80 peer-reviewed publications and garnered more than 3000 citations.

Dr. Krockenberger’s research interests encompass a wide range of topics within the field of molecular beam epitaxy of complex transition metal oxides and nitrides. His investigations span from the exploration of novel superconductors and transmon Qubit devices to the study of ferromagnets and multiferroic materials. A key motivation for his work is to revolutionize the understanding and application of cuprate superconductors by constructing them using molecular beam epitaxy to create innovative superlattices. Through his innovative research, Dr. Krockenberger is pushing the boundaries of materials science and contributing to the development of transformative technologies.

Research Synopsis:

The discovery of high-temperature superconductivity in cuprates in 1986 ignited significant research into complex transition metal oxides. While 3d oxides have been extensively studied, 4d and 5d systems have been less explored due to challenges in achieving high-quality growth and controlling volatile oxide formation.

We have developed an electron-beam molecular beam epitaxy (EB-MBE) system equipped with electron impact emission spectrometry (EIES) for precise real-time control of elemental fluxes. This approach enables the synthesis of complex 4d and 5d transition metal oxides with tailored stoichiometries. To address the issue of volatile oxide formation, we employ a rate control system that compensates for element loss during oxidation.

To optimize the growth process, we have implemented a Bayesian optimization-based machine learning method. This approach allows for efficient exploration of the parameter space, enabling us to identify optimal growth conditions. By combining machine learning with EB-MBE, we can accelerate the discovery and synthesis of new materials with intriguing physical properties, such as palladates like Nd2−xCexPdO4.

A notable achievement is the synthesis of the first gold oxide, Sr5Au3O8, using molecular beam epitaxy. We will also discuss our recent progress in synthesizing complex osmates, a class of materials known for their high volatility and challenging growth conditions. Sr3OsO6, a double-perovskite related structure, exhibits the highest Curie temperature discovered so far among insulators. Our approach demonstrates the potential of EB-MBE and machine learning for exploring the frontiers of complex transition metal oxide materials science.