Direct observation of pinning of Abrikosov vortices in a specially inhomogenious crystal EuRbFe$_4$As$_4$

In the two-phase crystal EuRbFe$_4$As$_4$/EuRbFe$_2$As$_2$ (1144/122), a linear ordering of Abrikosov vortices, uncharacteristic for superconducting pnictides, has been found using the method of decorating with magnetic nanoparticles. The observed chains of vortices directed along crystallographic $\langle$110$\rangle$ axes of the orthorhombic EuRbFe$_2$As$_2$ phase are explained by pinning of vortices in the superconducting phase 1144 on linear defects associated with the twin boundaries of the non-superconducting 122 phase.