Physical properties of $A_x$Fe$_{2-y}$S$_2$ ($A$=K, Rb and Cs) single crystals

We successfully synthesized two new compounds Rb$_x$Fe$_{2-y}$S$_2$ and Cs$_x$Fe$_{2-y}$S$_2$ which were isostructural with K$_x$Fe$_{2-y}$Se$_2$ superconductor. We systematically investigated the resistivity, magnetism and thermoelectric power of $A_x$Fe$_{2-y}$S$_2$ ($A$=K, Rb and Cs) single crystals. High temperature resistivity and magnetic measurements show anomalies above 500 K depending on $A$ which are similar to $A_x$Fe$_{2-y}$Se$_2$. Discrepancy between ZFC and FC curves was observed in K$_x$Fe$_{2-y}$S$_2$ and Rb$_x$Fe$_{2-y}$S$_2$, while it disappears in Cs$_x$Fe$_{2-y}$S$_2$. Our results indicate the similar magnetism between $A_x$Fe$_{2-y}$S$_2$ and $A_x$Fe$_{2-y}$Se$_2$ at high temperature.