(Li0.84Fe0.16)OHFe0.98Sesuperconductor: Ion-exchange synthesis of large single-crystal and highly two-dimensional electron properties

Using a novel hydrothermal ion-exchange technique, large and high-quality optimally doped single crystals of the new superconductor (Li${}_{0.84}$Fe${}_{0.16}$)OHFe${}_{0.98}$Se have been successfully synthesized for the first time. Thanks to these single-crystal samples, the anomalous normal-state properties of a linear in-plane electric resistivity, a dip in the Hall coefficient, and a linear magnetic susceptibility are revealed for the first time.