Magnetic flux pinning effect, impurities

Magnetic flux pinning effect of impurities in copper oxide superconductors... 

In addition, we performed electronic state calculations for impurity atoms in Cu oxide superconductors in order to examine the effects of these impurities on the pinning of magnetic flux lines. For impurity atoms such as F substituting for O atoms, the contribution of the atomic orbitals of these atoms to HOMO is small and most of the charge carriers generally do not exist at the impurity sites. Impurity atoms such as F thus effectively pin magnetic flux lines in Cu oxide superconductors. 

With the use of the DV-Xa molecular orbital method, electronic structure calculations have been performed to investigate the impurity effect on material properties. Firstly, calculations were done for F atoms substituted for 0 (oxygen) atoms in copper oxide superconductors. It was found that the population of the atomic orbitals of F atoms is small in HOMO (highest occupied molecular orbital) and a small fraction of charge carriers enters the impurity sites. The F impurities are therefore expected to be effective for pinning magnetic flux lines in Cu oxide superconductors. 

In condensed matter physics, the effects of disorder, defects, and impurities are relevant for many materials properties hence their understanding is of utmost importance. The effects of randomness and disorder can be dramatic and have been investigated for a variety of systems covering a wide field of complex phenomena [109]. Examples include the pinning of an Abrikosov flux vortex lattice by impurities in superconductors [110], disorder in Ising magnets [111], superfluid transitions of He in a porous medium [112], and phase transitions in randomly confined smectic liquid crystals [113, 114]. 

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