Emerging Diluted Ferromagnetism in High‐T_c Superconductors Driven by Point Defect Clusters

Abstract

Defects in ceramic materials are generally seen as detrimental to their functionality and applicability. Yet, in some complex oxides, defects present an opportunity to enhance some of their properties or even lead to the discovery of exciting physics, particularly in the presence of strong correlations. A paradigmatic case is the high‐temperature superconductor YBa2Cu3O7‐δ (Y123), in which nanoscale defects play an important role as they can immobilize quantized magnetic flux vortices. Here previously unforeseen point defects buried in Y123 thin films that lead to the formation of ferromagnetic clusters embedded within the superconductor are unveiled. Aberration‐corrected scanning transmission microscopy has been used for exploring, on a single unit‐cell level, the structure and chemistry resulting from these complex point defects, along with density functional theory calculations, for providing new insights about their nature including an unexpected defect‐driven ferromagnetism, and X‐ray magnetic circular dichroism for bearing evidence of Cu magnetic moments that align ferromagnetically even below the superconducting critical temperature to form a dilute system of magnetic clusters associated with the point defects.

Direct observation of apical oxygen vacancies in the high-temperature superconductor YBa2Cu3O7−xHartman1, Mundet2, Idrobo3 et al. 2019Phys. Rev. MaterialsSelf Cite203180View full textAdd to dashboardCite

“…Optimal doping, at x = 0.07, gives a maximum T c of 92 K, while x > 0.55, destroys the superconducting state [1], thus controlling the oxygen stoichiometry allows a way to tune T c . J C is also modulated by the oxygen content, since the magnetic vortex pinning is sensitive to both the carrier concentration and the distortions around V O [2,3,5].…”

Atomic Structure and Electrical Activity of Grain Boundaries and Ruddlesden–Popper Faults in Cesium Lead Bromide Perovskite

“…Our DFT calculations indicate that neither the [001](210)∑5 GB nor the RP planar fault introduces any defect levels in the bandgap, as shown in the density of states (DOS) plots in Figure a. Since planar defects could serve as a sink for point defects and thus exhibit dynamic composition, we have examined several additional structures by introducing Cs and/or Br vacancies to the experimentally confirmed ∑5 GB and RP planar fault. One example for the ∑5 GB is shown in Figure b and a complete list can be found in Section S5 in the Supporting Information.…”

Controlling the strength of ferromagnetic order in YBa2Cu3O7/LaPrada1, Gaina2, Biškup3 et al. 2019Phys. Rev. B14050View full textAdd to dashboardCite

“…The interfaces appear coherent and mostly defect-free. Both A-and B-type YBCO layers exhibit a number of stacking faults in the form of Y-124-like double or even triple CuO chains (darker horizontal atomic planes) [39,40]. In the case of the A-type sample in Fig.…”