EAGER: Resolving the issue of pairing symmetry in Sr2RuO4

Non-technical description:Superconductivity is a macroscopic quantum phenomenon highly relevant to quantum computing and other quantum technologies. The drive towards quantum computing calls for deeper understanding of the fundamental physics of superconductivity. For example, the implementation of fault tolerant topological quantum computing may be achievable with exotic spin-triplet superconductors. Single-layer strontium ruthenate (SRO) had been a leading candidate for a spin-triplet superconductor up to 2019. However, it turned out that one of the experiments that supported that claim in SRO is incorrect. This led to a controversy on the nature of superconductivity in this material. This experimental and theoretical project will aim to address this controversy as well as train future scientists from underrepresented minority communities in STEM to help meet the human resource needs of emerging quantum technologies.Technical description:The symmetry properties of the superconducting order parameter, which consists of orbital and spin parts, are of fundamental interest for superconductivity research. Single-layer strontium ruthenate (SRO) was considered a leading candidate for spin-triplet superconductivity up to 2019 when results from an important NMR Knight shift experiment from 1998, which probes the spin part of the order parameter, was shown to be incorrect. This led to suggestions by some researchers that SRO is actually a spin singlet. On the other hand, the Josephson effect based phase-sensitive experiments on SRO, which have remained largely unchallenged, suggest that the orbital part of the order parameter in SRO is of an odd parity, which implies that SRO is a spin triplet due to the presence of an inversion symmetry in this material. The heated debate on the pairing symmetry in SRO calls for new theoretical insights and additional experimental inputs. This project aims to strengthen the previous determination of the odd parity order parameter in SRO as well as identify ways to reconcile this with work probing the spin degrees of freedom.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.