Melting of vortex lattice in the magnetic superconductor RbEuFe4As4

Thermal fluctuations always melt the vortex lattice in type-II superconductors at temperatures below the mean-field transition. The extent of the intermediate vortex-liquid state varies widely among different materials. Exploring the vortex-lattice melting in the magnetic iron arsenide RbEuFe${}_{4}$As${}_{4}$ via calorimetry and transport, the authors demonstrate here that the vortex liquid occupies a significant portion of the phase diagram and that the location of the melting line agrees with theoretical predictions without fitting parameters. Comparison with other materials reveals the universality of melting behavior.