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Quasi-one-dimensional vortex matter in superconducting nanowires
It is well known that superconducting films made of a type-I material can demonstrate a type-II magnetic
response, developing stable vortex configurations in a perpendicular magnetic field. Here we show that the
superconducting state of a type-I nanowire undergoes more complex transformations, depending on the nanowire
thickness. Sufficiently thin nanowires deviate from type I and develop multiquantum vortices and vortex clusters
similar to intertype (IT) vortex states in bulk superconductors between conventional superconductivity types
I and II. When the nanowire thickness decreases further, the quasi-one-dimensional vortex matter evolves
towards type II so that the IT vortex configurations gradually disappear in favor of the standard Abrikosov
lattice (chain) of single-quantum vortices. However, type II is not reached. Instead, an ultrathin nanowire
re-enters abruptly the type-I regime while vortices tend to be suppressed by the boundaries, eventually becoming
one-dimensional phase-slip centers. Our results demonstrate that arrays of nanowires can be used to construct
composite superconducting materials with a widely tunable magnetic response.