High Pressure Transport and Structural Study on the Honeycomb Lattice Iridates $A_2$IrO$_3$ ($A =$ Na, Li)

The honeycomb lattice iridates $A_2$IrO$_3$ ($A =$ Na, Li) have been predicted and shown to exhibit novel magnetic properties which suggest that these materials could realize bond-directional Kitaev-like magnetic exchange interactions [1 - 5]. We will present high pressure (P) electrical transport ($P \leq 80$~GPa) and powder X-ray diffraction ($P \leq 40$~GPa) on these materials. The PXRD data for both materials show a structural transition around $P \sim 5$~GPa. The transport data show a dramatic reduction of the charge gap for Na$_2$IrO$_3$. References: [1] J. Chaloupka, G. Jackeli, and G. Khaliullin, Phys. Rev.Lett. {\bf 105}, 027204 (2010). [2] Y. Singh and P. Gegenwart, Phys. Rev. B {\bf 82}, 064412 (2010). [3] Y. Singh et al., Phys. Rev. Lett. {\bf 108}, 127203 (2012). [3] F. Ye et al., Phys. Rev. B {\bf 85}, 180403 (2012) [5] S. H. Chun et al. Nature Phys. {\bf 11}, 462 (2015).