Biomedical subjects

M Menghini

Publications and source records attributed to M Menghini.

3 recordsLinked to original sources

PubMed2005

Commensurability and stability in nonperiodic systems.

We have investigated the response of 3D Bi(2)Sr(2)CaCu(2)O(8) vortex structures to a weak perturbation induced by 2D Fe pinning structures acting on one extremity of vortex lines. The pinning patterns were nano-engineered at the sample surface by means of either a Bitter decoration of the vortex lattice or electron-beam lithography. The commensurability conditions between 2D rigid pinning potentials and 3D elastic structures with short-range positional and long-range orientational correlation have been experimentally determined. When the 2D potential is a replica of the nonperiodic vortex structure an amplification of its interaction with the vortex structure takes place. This effect is detected only for the first matching field, becoming negligible for other matching fields. On the other hand, a periodic 2D perturbation is shown to transform the nonperiodic Bragg glass-like structure into an Abrikosov crystal with an effective Debye-Waller factor.

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PubMed2003

First-order phase transition from the vortex liquid to an amorphous solid.

We present a systematic study of the topology of the vortex solid phase in superconducting Bi2Sr2CaCu2O8 samples with low doses of columnar defects. A new state of vortex matter imposed by the presence of geometrical contours associated with the random distribution of columns is found. The results show that the first-order liquid-solid transition in this vortex matter does not require a structural symmetry change.

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PubMed2003

Melting of "porous" vortex matter.

Bitter decoration and magneto-optical studies reveal that in heavy-ion irradiated superconductors, a "porous" vortex matter is formed when vortices outnumber columnar defects. In this state ordered vortex crystallites are embedded in the "pores" of a rigid matrix of vortices pinned on columnar defects. The crystallites melt through a first-order transition while the matrix remains solid. The melting temperature increases with density of columnar defects and eventually turns into a continuous transition. At high temperatures a sharp kink in the melting line is found, signaling an abrupt change from crystallite melting to melting of the rigid matrix.

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