In-situ local imaging of ferromagnetism and superconductivity in RbEuFe${}_4$As${}_4$

Abstract

The coexistence of superconductivity and ferromagnetism is an intrinsically interesting research focus in condensed matter physics but the study is limited by low superconducting ($T_c$) and magnetic ($T_m$) transition temperatures in related materials. Here, we used a scanning superconducting quantum interference device to image the in-situ diamagnetic and ferromagnetic responses of RbEuFe${}_4$As${}_4$ with high $T_c$ and $T_m$. We observed significant suppression of superfluid density in vicinity of the magnetic phase transition, signifying fluctuation-enhanced magnetic scatterings between Eu spins and Fe 3$d$ conduction electrons. Intriguingly, we observed multiple ferromagnetic domains which should be absent in an ideal magnetic helical phase. The formation of these domains demonstrates a weak $c$-axis ferromagnetic component probably arising from Eu spin-canting effect, indicative of possible superconductivity-driven domain Meissner and domain vortex-antivortex phases as revealed in EuFe${}_2$(As${}_{0.79}$P${}_{0.21}$)${}_2$. Our observations highlight RbEuFe${}_4$As${}_4$ is a unique system which includes multiple interplay channels between superconductivity and ferromagnetism.

11 pages, 5 figures

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