Quantum materials have attracted much attention in recent years due to their exotic and intriguing properties, which may also result in new concepts in quantum devices. Transition metal oxides in (111) orientation have recently gained special interest owing to a combination of several factors. It has a hexagonal crystal structure which is very similar to graphene, topological insulator Bi2Se3, and transition metal dichalcogenides known as 2D materials, which are currently in forefront of fundamental research. On the other hand, the system also possesses strong electron-electron correlation and large spin-orbit coupling, two of the major interactions which are hallmark of quantum materials. Theoretical calculations have predicted that these interactions together may lead to topological band, a new type of electron phase identified in recent years, and a variety of exotic quantum phases. To study these interactions and realize the rich new phases will significantly enhance our understanding of the phenomena in quantum states and contribute to the development of this emergent research area.
The objective of this project is to study the interplay between superconductivity, Rashba spin orbit coupling, topological bands, and Landau level states, a quantized energy band in high magnetic fields, in SrTiO3 (111) based high mobility electron systems. SrTiO3 is a band insulator. However, at the interface of SrTiO3 with another insulator, it may form high mobility highly conducting electron systems. The interface quantum well has a honeycomb lattice structure, very similar to graphene and 2D materials. On the other hand, it also has strong on-site Coulomb interaction and strong Rashba spin orbit coupling (SOC) that the others do not have in its single layer form. In addition, it is also a superconductor with co-existence of superconductivity and ferromagnetism. These characters make it a unique system to study the rich quantum phenomena. A room temperature fabrication process has been developed previously in our group which can produce high mobility interface 2D electron systems based on SrTiO3 single crystal and amorphous insulators with controllable carrier densities and dimensionality. At high magnetic field, the lowest Landau level can be reached where only the lowest Landau energy state is occupied and all states above are empty. This provides a fascinating platform to study the emergent phenomena resulted from the interaction between quantum states, competing interactions, and superconductivity. We plan to study two specific areas (1) The nature of the superconductivity in the low carrier concentration electron systems, the influence of Rashba spin orbit coupling on the superconductivity, and the influence of the magnetic phase on the superconductivity; (2) Interaction of superconductivity with low Landau level quantum states where the fully occupied and half-filled state can be tuned by magnetic fields. These will be studied with a superconductor nanoscale contact. A high Tc and high Hc2 superconductor MgB2 (Tc ~ 40 K) will be used for the superconducting contact to ensure that the superconductor will still be in the superconducting state at high magnetic fields. Measurements at National High Magnetic Field Lab user facilities will also be part of the experiments in this project.
This project will have significant impact on the research fields. It is closely related to the active research in twisted graphene and bilayer 2D materials where rich quantum phenomena in high magnetic field are explored. This material however provides a different system with strong electron correlation and Rashba spin orbit coupling in the same regime. The results of the research will enhance our understanding of quantum materials due to strong competing interactions and will also have potential impact on the developing area of quantum devices.
