Structural Inhomogeneity in Oxide Superconductors

Superconductivity has been a major research topic for more than a century, yet in many important materials this macroscopic quantum phenomenon remains poorly understood. We have uncovered that superconductivity emerges in an unusual, yet remarkably universal manner upon cooling in three well-known families of complex oxides – strontium titanate, strontium ruthenate, and the cuprates – for which the origin of superconductivity is thought to differ [1]. This breakthrough was enabled by nonlinear magnetic response measurements, an innovative experimental approach that is uniquely sensitive to superconducting fluctuations. We find that the diamagnetic response above the bulk critical temperature Tc exhibits unusual exponential temperature dependence, with a characteristic temperature scale that differs from Tc. This scale correlates with the sensitivity of Tc to local stress, and it is influenced by intentionally induced structural disorder. Using diffuse neutron and X-ray scattering, we recently found further evidence that the universal electronic behavior is caused by intrinsic structural inhomogeneity that must be inherent to the oxides’ perovskite-based crystal structures [2]. The prevalence of such inhomogeneity has far-reaching implications for the interpretation of electronic properties of perovskites in general, including thin films and heterostructures. In the case of the cuprates, this inherent inhomogeneity constitutes a pivotal part of a robust phenomenological model that comprehensively captures hitherto elusive properties of the normal and superconducting states [3]. In the case of strontium titanate, these insights motivated a systematic study of plastically-deformed crystals that led to the discovery of remarkable superconductivity and ferroelectricity enhancements [4].

[1] D. Pelc et al., Nat. Commun. 10, 2729 (2019)
[2] D. Pelc et al., arXiv:2103.05482
[3] D. Pelc et al., Sci. Adv. 5, eaau4538 (2019); Phys. Rev. B 102, 075114 (2020)
[4] S. Hameed et al., Nat. Mater. (2021) (https://doi.org/10.1038/s41563-021-01102-3)