Yasumoto Tanaka

A local minimum state, energetically inequivalent to the global minimum, can emerge in a coupled-frustrated multi-component superconductor. This local minimum state is metastable when it occupies the entire system. However, when a global-minimum domain appears within the metastable state, this local minimum appears only as an energetically higher domain, which nevertheless constitutes a physically meaningful configuration within the vacuum hierarchy. In this context, the metastable local minimum can be interpreted as a false vacuum, whereas the global minimum represents the true vacuum.

An ultrathin superconducting bilayer creates a coreless fractional vortex when only the second layer has a hole. The quantization is broken by the hole, and the normal core disappears. The magnetic flux is no longer confined near the normal core, and its density profile around the hole becomes similar to that of a cr\`eme caramel; the divergence of the magnetic flux density is truncated around the center. We propose basic design of a practical device to realize a coreless fractional vortex.