Superconducting Instabilities in Strongly Correlated Infinite-Layer Nickelates.

The discovery of superconductivity in infinite-layer nickelates has added a new family of materials to the fascinating growing class of unconventional superconductors. By incorporating the strongly correlated multiorbital nature of the low-energy electronic degrees of freedom, we compute the leading superconducting instability from magnetic fluctuations relevant for infinite-layer nickelates. Specifically, by properly including the doping dependence of the Ni d_{x^{2}-y^{2}} and d_{z^{2}} orbitals as well as the self-doping band, we uncover a transition from d-wave pairing symmetry to nodal s_{±} superconductivity, driven by strong fluctuations in the d_{z^{2}}-dominated orbital states. We discuss the properties of the resulting superconducting condensates in light of recent tunneling and penetration depth experiments probing the detailed superconducting gap structure of these materials.

Raising the Critical Temperature by Disorder in Unconventional Superconductors Mediated by Spin Fluctuations.

We propose a mechanism whereby disorder can enhance the transition temperature T_{c} of an unconventional superconductor with pairing driven by exchange of spin fluctuations. The theory is based on a self-consistent real space treatment of pairing in the disordered one-band Hubbard model. It has been demonstrated before that impurities can enhance pairing by softening the spin fluctuations locally; here, we consider the competing effect of pair breaking by the screened Coulomb potential also present. We show that, depending on the impurity potential strength and proximity to magnetic order, this mechanism results in a weakening of the disorder-dependent T_{c}-suppression rate expected from Abrikosov-Gor'kov theory, or even in disorder-generated T_{c} enhancements.