Twists, Turns, and Bumps on the Road to Nickelate Superconductivity
Dr. John F. Mitchell
Materials Science Division
Argonne National Laboratory
The field of superconductivity is occasionally jolted with unexpected and transformational discoveries, most of the time by the appearance of new materials. The most famous of these being the high-Tc cuprates from nearly 40 years ago and the iron-based systems just over 15 years ago. A more recent example has been the advent of superconductivity in nickel-based oxides, which were hypothesized alongside the cuprates, but only in the past five years realized experimentally. Nickelate superconductivity has been found in three materials classes: thin film “infinite layer” materials typified by (Nd,Sr)NiO2, in thin multilayer analogs, and more recently in bulk crystals of Ruddlesden-Popper (R-P) phases such as bilayer La3Ni2O7 (La-327) and trilayer La4Ni3O10 (La- 4310), the latter two under high pressure (several GPa) conditions. Often, alongside the superconducting phase lie competing states that are almost as compelling as superconductivity, including proximate insulating phases where charge and spins are localized into ‘stripes,’ and associated insulator-metal transitions. Figuring out how to move these phases to the superconducting realm presents materials challenges. After giving a broad overview of the field and identifying gaps in our understanding, I will relate some of our adventures in the quest for superconductivity in bulk multilayer nickelates, exploration of competing phases, and finally the ‘hot’ Ruddlesden-Popper phases. I will emphasize materials issues/challenges that face the field (and call for caution when claiming ‘new physics’), the potential for new phases, and preview some new, preliminary results of another high pressure superconducting nickelate.
Hosted by Prof. Ghimire