Abstract
A pivotal challenge posed by unconventional superconductors is to unravel how superconductivity emerges upon cooling from the generally complex normal state. Here, we use nonlinear magnetic response, a probe that is uniquely sensitive to the superconducting precursor, to uncover remarkable universal behaviour in three distinct classes of oxide superconductors: strontium titanate, strontium ruthenate, and the cuprate high-Tc materials. We find unusual exponential temperature dependence of the diamagnetic response above the transition temperature Tc, with a characteristic temperature scale that strongly varies with Tc. We correlate this scale with the sensitivity of Tc to local stress and show that it is influenced by intentionally-induced structural disorder. The universal behaviour is therefore caused by intrinsic, self-organized structural inhomogeneity, inherent to the oxides’ perovskite-based structure. The prevalence of such inhomogeneity has far-reaching implications for the interpretation of electronic properties of perovskite-related oxides in general.
Highlights
A pivotal challenge posed by unconventional superconductors is to unravel how superconductivity emerges upon cooling from the generally complex normal state
Some of the most prominent unconventional superconductors are based on the perovskite crystal structure. This includes the materials we study here: SrTiO3 (STO), Sr2RuO4 (SRO), and the cuprates La2-xSrxCuO4 (LSCO) and HgBa2CuO4+δ (Hg1201). These oxides are of tremendous scientific interest: superconductivity in doped STO occurs at some of the lowest known charge carrier densities and, more than five decades after its discovery[1], there has been a recent upsurge of research activity[2,3,4]; SRO is a candidate for unconventional spin-triplet superconductivity[5]; LSCO and Hg1201 are archetypal cuprate high-Tc superconductors, arguably the most widely investigated class of quantum materials[6]
Superconducting transitions are clearly seen in linear response because of the diamagnetism associated with the superconducting state, but above Tc the properties of the non-superconducting normal state contribute to χ1
Summary
A pivotal challenge posed by unconventional superconductors is to unravel how superconductivity emerges upon cooling from the generally complex normal state. These oxides are of tremendous scientific interest: superconductivity in doped STO occurs at some of the lowest known charge carrier densities and, more than five decades after its discovery[1], there has been a recent upsurge of research activity[2,3,4]; SRO is a candidate for unconventional spin-triplet superconductivity[5]; LSCO and Hg1201 are archetypal cuprate high-Tc superconductors, arguably the most widely investigated class of quantum materials[6] These materials have widely different values of Tc, and, their respective superconducting pairing mechanisms remain unknown, they are thought to differ as well. The three different classes of oxide unconventional superconductors share a common precursor regime, with a likely origin in inherent inhomogeneity related to the common perovskite-based structure
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