12 research outputs found
Phase transition in a chain of quantum vortices
We consider interacting vortices in a quasi-one-dimensional array of
Josephson junctions with small capacitance. If the charging energy of a
junction is of the order of the Josephson energy, the fluctuations of the
superconducting order parameter in the system are considerable, and the
vortices behave as quantum particles. Their density may be tuned by an external
magnetic field, and therefore one can control the commensurability of the
one-dimensional vortex lattice with the lattice of Josephson junctions. We show
that the interplay between the quantum nature of a vortex, and the long-range
interaction between the vortices leads to the existence of a specific
commensurate-incommensurate transition in a one-dimensional vortex lattice. In
the commensurate phase an elementary excitation is a soliton, with energy
separated from the ground state by a finite gap. This gap vanishes in the
incommensurate phase. Each soliton carries a fraction of a flux quantum; the
propagation of solitons leads to a finite resistance of the array. We find the
dependence of the resistance activation energy on the magnetic field and
parameters of the Josephson array. This energy consists of the above-mentioned
gap, and also of a boundary pinning term, which is different in the
commensurate and incommensurate phases. The developed theory allows us to
explain quantitatively the available experimental data.Comment: 14 pages, 7 eps figure
Hall-conductivity sign change and fluctuations in amorphous NbGe films
The sign change in the Hall conductivity has been studied in thin amorphous
NbGe0.3) films. By changing the film thickness it is
shown that the field at which the sign reversal occurs shifts to lower values
(from above to below the mean-field transition field ) with increasing
film thickness. This effect can be understood in terms of a competition between
a positive normal and a negative fluctuation contribution to the Hall
conductivity.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Community and the creation of provincial identities: a re-interpretation of the aisled building at North Warnborough
The aisled hall at North Warnborough has attracted attention as one of a handful of examples frequently included in surveys and analyses of this common architectural type as well as for arguments related to the gendered use of space. This article presents a new architectural analysis of this building and attempts to set it within its immediate and wider archaeological and geological landscape context. A theoretically informed interpretation of the social significance of this site is offered, which has broader implications for the studies of Romano-British architecture, rural settlement, and landscape