Phase-Sensitive Measurements in Mesoscopic Nickelate Superconducting Junction Devices

Superconductivity is regarded as a fascinating manifestation of a macroscopic-scale quantum coherent state. The microscopic theories developed aiming to explain such phenomenon have largely irrigated other research fields spanning across condensed matter, particle and even nuclear physics. On the other hand, the understanding of unconventional superconductivity, which usually involves condensation of strongly correlated electrons into frictionless superfluid through unusual interactions, remains challenging. In particular, the mechanism of high-temperature superconductivity (HTS) since its discovery in copper oxides has been the ‘holy grail’ enigma in condensed matter physics for over 35 years. One promising strategy to unveil this long-standing puzzle is to search for superconducting layered oxides with similar electronic configuration to that of copper oxides. After a long and difficult campaign, the discovery of superconducting infinite-layer (IL) nickelates as a new class of unconventional superconductors has furthered this quest and engendered a novel paradigm for understanding HTS. To this end, investigation of the symmetry of the pairing state in IL nickelates has proven to be an indispensable approach to unravelling the underlying physics of the pairing mechanism; however, due to the significant challenges in materials synthesis and despite attempts using indirect approaches, a clear demonstration of the symmetry of the superconducting order parameter of nickelates is still elusive. In this project, we propose to use high-quality IL nickelate films grown in our laboratory to form different superconducting mesoscopic devices for phase-sensitive experiments. Across these measurements, we plan to leverage superconducting quantum coherence of the pairing electrons in these devices for providing compelling evidence on the pairing-state symmetry. This proposal is built upon two extraordinary qualities: (1) our unique strength in growth of top-crystallinity thin films of superconducting IL nickelates; (2) our special expertise and excellent existing resources on device fabrication and quantum transport measurements of junctions. The key to the success of this proposed research largely relies on a seamless coordination of tasks at research fronts of both synthesis and measurements, for which we are immensely well positioned. Though collaborations, we will establish close-loop feedback between materials perfection, device quality control and high-precision measurements. This project will answer key questions on the pairing symmetry of the superconducting nickelates, marking impactful footsteps towards understanding the nature of pairing interactions in unconventional superconductivity.