Effect of high-intensity ultrasound on superconducting properties of polycrystalline YBCO

High intensity ultrasonic irradiation (sonication) of alkane slurries of polycrystalline \ybco leads to a significant modification of the grain morphology and, if performed with enforced oxygen flow, results in the increase of the superconducting transition temperature. Sonication with added Fe(CO)$_5$ produces magnetic \fe2o3 nanoparticles deposited on the surface of \ybco (YBCO) granules. Upon sintering these nanoparticles should act as efficient pinning centers utilizing both condensation and magnetic contributions to the free energy. The developed method could become a major technique to produce practically useful high-pinning nanocomposite materials based on \ybco superconductor.Comment: to be presented at LT-25 conferenc

Campbell Penetration Depth of a Superconductor in the Critical State

The magnetic penetration depth $\lambda(T,H,j)$ was measured in the presence of a slowly relaxing supercurrent, $j$. In single crystal $\mathrm{Bi_2Sr_2CaCu_2O_8}$ below approximately 25 K, $\lambda(T,H,j)$ is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as $j$ changes. The Campbell length depends upon the ratio $j/j_{c}$ where $j_{c}$ is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor

Low temperature vortex phase diagram of Bi2Sr2CaCu2O8 : a magnetic penetration depth study

We report measurements of the magnetic penetration depth \lambda_m(T) in the presence of a DC magnetic field in optimally doped BSCCO-2212 single crystals. Warming, after magnetic field is applied to a zero-field cooled sample, results in a non-monotonic \lambda_m(T), which does not coincide with a curve obtained upon field cooling, thus exhibiting a hysteretic behaviour. We discuss the possible relation of our results to the vortex decoupling, unbinding, and dimensional crossover.Comment: M2S-HTSC-V

Off-axis electron holography of bacterial cells and magnetic nanoparticles in liquid

The mapping of electrostatic potentials and magnetic fields in liquids usingelectron holography has been considered to be unrealistic. Here, we showthat hydrated cells ofMagnetospirillum magneticumstrain AMB-1 and assem-blies of magnetic nanoparticles can be studied using off-axis electronholography in a fluid cell specimen holder within the transmission electronmicroscope. Considering that the holographic object and reference waveboth pass through liquid, the recorded electron holograms show sufficientinterference fringe contrast to permit reconstruction of the phase shift ofthe electron wave and mapping of the magnetic induction from bacterialmagnetite nanocrystals. We assess the challenges of performingin situmagne-tization reversal experiments using a fluid cell specimen holder, discussapproaches for improving spatial resolution and specimen stability, and outlinefuture perspectives for studying scientific phenomena, ranging from interpar-ticle interactions in liquids and electrical double layers at solid–liquidinterfaces to biomineralization and the mapping of electrostatic potentialsassociated with protein aggregation and folding