Nicola Poccia

Scale-free structural organization of oxygen interstitials in La2CuO4+y

It is well known that the microstructures of the transition-metal oxides, including the high-transition-temperature (high-Tc) copper oxide superconductors, are complex. This is particularly so when there are oxygen interstitials or vacancies, which influence the bulk properties. For example, the oxygen interstitials in the spacer layers separating the superconducting CuO2 planes undergo ordering phenomena in Sr2O1+yCuO2 (ref. 9), YBa2Cu3O6+y (ref. 10) and La2CuO4+y (refs 11–15) that induce enhancements in the transition temperatures with no changes in hole concentrations. It is also known that complex systems often have a scale-invariant structural organization, but hitherto none had been found in high-Tc materials. Here we report that the ordering of oxygen interstitials in the La2O2+y spacer layers of La2CuO4+y high-Tc superconductors is characterized by a fractal distribution up to a maximum limiting size of 400 μm. Intriguingly, these fractal distributions of dopants seem to enhance superconductivity at high temperature.

Nanoscale phase separation in the iron chalcogenide superconductor K 0 . 8 Fe 1 . 6 Se 2 as seen via scanning nanofocused x-ray diffraction

Advanced synchrotron radiation focusing down to a size of 300 nm has been used to visualize nanoscale phase separation in the K

Evolution and control of oxygen order in a cuprate superconductor

{}_{0.8}

Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor.

Fe

Optimum inhomogeneity of local lattice distortions in La2CuO4+y

{}_{1.6}

Resonant and crossover phenomena in a multiband superconductor: Tuning the chemical potential near a band edge

Se

Model for phase separation controlled by doping and the internal chemical pressure in different cuprate superconductors

{}_{2}

Imaging and control of ferromagnetism in LaMnO3/SrTiO3 heterostructures

superconducting system using scanning nanofocus single-crystal x-ray diffraction. The results show an intrinsic phase separation in K

Shape resonance for the anisotropic superconducting gaps near a Lifshitz transition: the effect of electron hopping between layers

{}_{0.8}

Multiscale distribution of oxygen puddles in 1/8 doped YBa2Cu3O6.67.

Fe