Intermittent superconductivity and unconventional vortex configurations in nanoscale superconducting noncircular systems

The flux-dependent evolution of vortex states in nanoscale superconducting noncircular systems is investigated based on the Bogoliubov-de Gennes theory. For a superconductor with the coherence length comparable to the Fermi wavelength, the spatial variations of the superconducting order parameter are very sensitive to the finite size of the sample. With increasing the applied flux, the superconducting state and the normal state can alternately appear in small squares, and a remarkable intermittent superconducting behavior for the ground-state transition is found. Moreover, when the square size is enlarged, the asymmetric single-vortex and multivortex states as well as the vortex-antivortex pairs can emerge as the metastable or ground states, arising from the effect of strong quantum confinement.