Authors: V. S. Stolyarov, A. Casano, M. A. Belyanchikov, A. S. Astrakhantseva, S. Yu. Grebenchuk, D. S. Baranov, I. A. Golovchanskiy, I. Voloshenko, E. S. Zhukova, B. P. Gorshunov, A. V. Muratov, V. V. Dremov, L. Ya. Vinnikov, D. Roditchev, Y. Liu, G.-H. Cao, M. Dressel, and E. Uykur
Phys. Rev. B volume 98, 140506(R)
Abstract: Transport, magnetic, and optical investigations on EuRbFe4As4 single crystals evidence that the ferromagnetic ordering of the Eu2+ magnetic moments at Tm=15 K, below the superconducting transition (Tc=36 K), affects superconductivity in a weak but intriguing way. Upon cooling below Tm, the zero resistance state is preserved and the diamagnetic response is only slightly affected by the emerging ferromagnetism; a perfect diamagnetism is recovered at low temperatures. The infrared conductivity is strongly suppressed in the far-infrared region below Tc, associated with the opening of a complete superconducting gap at 2Δ=10 meV. A gap smaller than the weak-coupling limit suggests strong orbital effects or, within a multiband superconductivity scenario, the existence of a larger yet unrevealed gap.