Controlling Magnetism, Metal-Insulator Transitions, and Superconductivity in Ruthenate Thin Films

Cornell University, Ithaca NY

Investigators

Abstract

Non-Technical Abstract: The electronic and magnetic properties of materials form the backbone of modern technologies, including computer processors, telecommunications, information storage, and displays. Moreover, the ability to deterministically control these properties, for instance, in semiconductor transistors, is one of the crowning achievements of materials physics in the past fifty years and has had enormous societal and economic impacts. However, the end of Moore's Law and the increasing need for smaller, faster, and more power efficient electronics demands the search for new electronic materials that can ultimately replace existing materials such as silicon and copper which have been in use for nearly half a century. This project aims to investigate one class of electronic materials comprised of ruthenium oxides which exhibit a tremendous variety of electronic and magnetic properties, some of which could be potentially important for a wide range of applications including quantum computing, non-volatile memories, and sensing. These materials are synthesized as thin films which are only a few atoms thick, and their properties are manipulated by controlling the thickness of the film or stretching the bonds between atoms. Advanced spectroscopic tools allow for a more detailed understanding of how to better optimize and control their desired properties. Finally, this project provides crucial training to young scientists in materials synthesis and characterization, and the samples fabricated in these studies support a number of scientific collaborations both nationwide and internationally. Technical Abstract: A major challenge in condensed matter physics is to control the many-body interactions in correlated quantum materials with the objective of being able to engineer their properties in a deterministic fashion. The potential for quantum materials as platforms for future technologies such as topological quantum computation or memories has motivated an effort to discover new avenues to measure and manipulate their electronic and magnetic structure. The strategy outlined in this proposal is to use the family of layered ruthenates which exhibit a range of emergent electronic and magnetic phenomena, including spin-triplet superconductivity, electronic nematicity, quantum criticality, and metal-insulator transitions, as a platform for manipulating electronic and magnetic properties through epitaxial strain, particularly since the properties of ruthenates are particularly responsive to small perturbations. This project combines oxide molecular beam epitaxy growth and in situ high-resolution angle-resolved photoemission to investigate the electronic structure of the ruthenates, and how the band structure and Fermi surfaces responds to strain. Graduate students involved in this project are trained in molecular beam epitaxy growth, photoemission spectroscopy, and a multitude of sample characterization techniques. Some specific objectives of this work include increasing the superconducting Tc of Sr2RuO4 via epitaxial strain, and gaining insight into the mechanism of spin-triplet superconductivity by correlating Tc with changes in the Fermi surface topology. Another goal is to control the magnetic field driven quantum phase transition in Sr3Ru2O7 by changing the RuO6 octahedral rotation angles through epitaxial strain, and correlating these behaviors with changes in the electronic structure.