Title: Superconductivity at 33 - 37 K in $ALn_2$Fe$_4$As$_4$O$_2$ ($A$ = K and Cs; $Ln$ = Lanthanides),
Abstract: We have synthesized 10 new iron oxyarsenides, K$Ln_2$Fe$_4$As$_4$O$_2$ ($Ln$
= Gd, Tb, Dy, and Ho) and Cs$Ln_2$Fe$_4$As$_4$O$_2$ ($Ln$ = Nd, Sm, Gd, Tb, Dy,
and Ho), with the aid of lattice-match [between $A$Fe$_2$As$_2$ ($A$ = K and
Cs) and $Ln$FeAsO] approach. The resultant compounds possess hole-doped
conducting double FeAs layers, [$A$Fe$_4$As$_4$]$^{2-}$, that are separated by
the insulating [$Ln_2$O$_2$]$^{2+}$ slabs. Measurements of electrical
resistivity and dc magnetic susceptibility demonstrate bulk superconductivity
at $T_\mathrm{c}$ = 33 - 37 K. We find that $T_\mathrm{c}$ correlates with the
axis ratio $c/a$ for all 12442-type superconductors discovered. Also,
$T_\mathrm{c}$ tends to increase with the lattice mismatch, implying a role of
lattice instability for the enhancement of superconductivity.