New Macroscopic Quantum Effect in a Type-II Superconductor

A series of structures is observed in the field dependence of the current threshold of a type-II superconductor in a longitudinal magnetic field. In the mixed state the structures appear in the field $H=\frac{H_{c2\mathrm{}}}{N}$ ($H_{c2\mathrm{}}$ is the upper critical field; $N$ is an integer), while for the case $H>\mathrm{}{H}_{c2\mathrm{}}$, they are observed when $H=N^{\frac{1}{2}}{H}_{c2\mathrm{}}$. These phenomena are discussed on the basis of the Ginzburg-Landau equation. The experimental data in the mixed state are interpreted as evidence for the existence of some new quantum states other than the Abrikosov state.