Influence of non-magnetic dilution in honeycomb-lattice iridates A$_2$IrO$_3$ (A=Na,Li)*

Honeycomb-lattice iridates A$_2$IrO$_3$ (A= Na,Li) display a spin-orbit Mott insulating state [1,2] and have been proposed as experimental realizations for the Kitaev-Heisenberg(KH) model[1] or a novel kind of quasi-molecular orbital(QMO) system [3]. Recently it has been proposed, that dilution of the Ir$^{4+}$ moments could be used to investigate the importance of next neighbor interactions (HK model) versus further next neighbor interactions (J1-J2-J3 model)[4]. We have synthesized A$_2$(Ir$_{1-x}$Ti$_x$)O$_3$ single- and polycrystals for the Na and Li system, respectively and investigated their magnetic and thermodynamic properties. Even very low Ti$^{4+}$ substitution leads to spin glassy behavior and spin glass temperature (T$_g$) is steeply suppressed towards the percolation threshold. This confirms that frustrated nearest-neighbor interactions are the most important factor to set up the magnetism in A$_2$IrO$_3$.\\[4pt] [1] Y.Singh et.al. - PRL 108, 127203 (2012).\\[0pt] [2] H. Gretarsson et.al. - PRL 110, 076402 (2013).\\[0pt] [3] I. Mazin et.al. - PRL 109, 197201 (2012).\\[0pt] [4] Eric C. Andrade et.al. - arxiv 1309.2951.