THESIS
2015
xvi, 132 pages : illustrations (some color) ; 30 cm
Abstract
In this PhD project, the feasibility of establishing a state with vanishing resistance in quasi-1D
superconductors are studied. In the first stage, extrinsic quasi-1D superconductors based on
composite materials made by metallic nanowire arrays embedded in mesoporous silica substrates,
such as Pb-SBA-15 and NbN-SBA-15 (fabricated by a Chemical Vapor Deposition technique) are
investigated. Two impressive outcomes in Pb-SBA-15 are found, including an enormous
enhancement of the upper critical field from 0.08T to 14T and an increase of the superconducting
transition temperature onset s from 7.2 to 11K. The second stage is to apply Monte Carlo
simulations to model the quasi-1D superconductor, considering its penetration depth, coherence
length, defects, electron mean free path, tunn...[
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In this PhD project, the feasibility of establishing a state with vanishing resistance in quasi-1D
superconductors are studied. In the first stage, extrinsic quasi-1D superconductors based on
composite materials made by metallic nanowire arrays embedded in mesoporous silica substrates,
such as Pb-SBA-15 and NbN-SBA-15 (fabricated by a Chemical Vapor Deposition technique) are
investigated. Two impressive outcomes in Pb-SBA-15 are found, including an enormous
enhancement of the upper critical field from 0.08T to 14T and an increase of the superconducting
transition temperature onset s from 7.2 to 11K. The second stage is to apply Monte Carlo
simulations to model the quasi-1D superconductor, considering its penetration depth, coherence
length, defects, electron mean free path, tunneling barrier and insulating width between the
nanowires. The Monte Carlo results provide a clear picture to approach to stage 3, which
represents a study of the intrinsic quasi-1D superconductor Sc
3CoC
4, which contains parallel
arrays of 1D superconducting CoC
4 ribbons with weak transverse Josephson or Proximity
interaction, embedded in a Sc matrix. According to our previous work, a BKT transition in the
lateral plane is believed to be the physics behind the vanishing resistance of quasi-1D
superconductors, because it activates a dimensional crossover from a 1D fluctuating
superconductivity at high temperature to a 3D bulk phase coherent state in the entire material at
low temperatures. Moreover, we decided to study thin 1D Sn nanowires without substrate, which
display very similar superconducting properties to Pb-SBA-15 with a strong critical field and T
c
enhancement. Finally, a preliminary research on a novel quasi-2D superconductor formed by
parallel 2D mercury sheets that are separated by organic molecules is presented. The latter
material may represent a model system to study the effect of a layered structure, which is believed
to be an effective ingredient to design high temperature superconductors.
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