Superstripes and complexity in high-temperature superconductors

While for many years the lattice, electronic and magnetic complexity of high-temperature superconductors (HTS) has been considered responsible for hindering the search of the mechanism of HTS now the complexity of HTS is proposed to be essential for the quantum mechanism raising the superconducting critical temperature. The complexity is shown by the lattice heterogeneous architecture: a) heterostructures at atomic limit; b) electronic heterogeneity: multiple components in the normal phase; c) superconducting heterogeneity: multiple superconducting gaps in different points of the real space and of the momentum space. The complex phase separation forms an unconventional granular superconductor in a landscape of nanoscale superconducting striped droplets which is called the "superstripes" scenario. The interplay and competition between magnetic orbital charge and lattice fluctuations seems to be essential for the quantum mechanism that suppresses thermal decoherence effects at an optimum inhomogeneity.Comment: 20 pages, 3 figures; J. Supercon. Nov. Mag. 201

The polarisation properties of the HD 181327 debris ring: Evidence for sub-micron particles from scattered light observations

Context: Polarisation is a powerful remote-sensing tool to study the nature of particles scattering the starlight. It is widely used to characterise interplanetary dust particles in the Solar System and increasingly employed to investigate extrasolar dust in debris discs’ systems. Aims: We aim to measure the scattering properties of the dust from the debris ring around HD 181327 at near-infrared wavelengths. Methods: We obtained high-contrast polarimetric images of HD 181327 in the H band with the SPHERE/IRDIS instrument on the Very Large Telescope (ESO). We complemented them with archival data from HST/NICMOS in the F 110W filter reprocessed in the context of the Archival Legacy Investigations of Circumstellar Environments (ALICE) project. We developed a combined forward-modelling framework to simultaneously retrieve the scattering phase function in polarisation and intensity. Results: We detected the debris disc around HD 181327 in polarised light and total intensity. We measured the scattering phase function and the degree of linear polarisation of the dust at 1.6 µm in the birth ring. The maximum polarisation is 23.6% ± 2.6% and occurs between a scattering angle of 70° and 82°. Conclusions: We show that compact spherical particles made of a highly refractive and relatively absorbing material in a differential power-law size distribution of exponent −3.5 can simultaneously reproduce the polarimetric and total intensity scattering properties of the dust. This type of material cannot be obtained with a mixture of silicates, amorphous carbon, water ice, and porosity, and requires a more refracting component such as iron-bearing minerals. We reveal a striking analogy between the near-infrared polarisation of comets and that of HD 181327. The methodology developed here combining VLT/SPHERE and HST/NICMOS may be applicable in the future to combine the polarimetric capabilities of SPHERE with the sensitivity of JWST.ISSN:0004-6361ISSN:1432-074