Microscopic description of intermediate mixed state in superconductors between the first and second types

It has long been known that superconductors in the crossover between superconductivity types I and II exhibit an intermediate mixed state (IMS) with exotic flux configurations such as vortex clusters and chains. Achieving a comprehensive microscopic description of the vortex configurations within this intertype region has proven elusive until now due to the large computational demands involved. We have addressed this long-standing problem by presenting microscopic calculations of the IMS configurations. Our calculations, performed at zero temperature, reveal key features of the IMS, including the formation of vortex clusters and the multivortex nature of interactions between vortices. The obtained boundaries of the IT domain reproduce existing experimental observations remarkably well. Also, the results match earlier findings obtained using the perturbation theory in the vicinity of the critical temperature.