Quantum Spin Liquid in a depleted triangular lattice Iridate K$_x$Ir$_y$O$_2$

Abstract: We report discovery of a new iridate family K$<em>x$Ir$_y$O$_2$ with depleted triangular lattice planes made up of edge sharing IrO$_6$ octahedra separated by K planes. Such a material interpolates between the triangular and honeycomb lattices and is a new playground for Kitaev physics. The materials are Mott insulators with $y = 1 - x/4$. Physical property measurements for the $x \approx 0.85$ material are reported. Using magnetic susceptibility $\chi$ versus temperature $T$ measurements we find $S</em>{eff} = 1/2$ moments interacting strongly with a Weiss temperature $\theta \approx - 180$~K and no magnetic order or spin freezing down to $T = 1.8$~K\@. Heat capacity shows a broad maximum around $30$~K which is insensitive to magnetic fields and a $T$-linear low temperature behaviour with $\gamma \sim 10$~mJ/mol~K$<sup>2$. These results are consistent with a gapless QSL state in K$<em>{0.85}$Ir$</em>{0.79}$O$_2$.