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arXiv · 1905.12456

Optical signature of the pressure-induced dimerization in the honeycomb iridate $\alpha$-Li$_2$IrO$_3$

V. Hermann·J. Ebad-Allah·F. Freund·A. Jesche·A. A. Tsirlin·P. Gegenwart·C. A. Kuntscher
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Abstract

We studied the effect of external pressure on the electrodynamic properties of $\alpha$-Li$_2$IrO$_3$ single crystals in the frequency range of the phonon modes and the Ir $d$-$d$ transitions. The abrupt hardening of several phonon modes under pressure supports the onset of the dimerized phase at the critical pressure $P_c$=3.8 GPa. With increasing pressure an overall decrease in spectral weight of the Ir $d$-$d$ transitions is found up to $P_c$. Above $P_c$, the local (on-site) $d$-$d$ excitations gain spectral weight with increasing pressure, which hints at a pressure-induced increase in the octahedral distortions. The non-local (intersite) Ir $d$-$d$ transitions show a monotonic blue-shift and decrease in spectral weight. The changes observed for the non-local excitations are most prominent well above $P_c$, namely for pressures $\geq$12 GPa, and only small changes occur for pressures close to $P_c$. The profile of the optical conductivity at high pressures ($\sim$20 GPa) appears to be indicative for the dimerized state in iridates.

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V. Hermann, J. Ebad-Allah, F. Freund, A. Jesche, A. A. Tsirlin, P. Gegenwart, C. A. Kuntscher. 2019-05-29. Optical signature of the pressure-induced dimerization in the honeycomb iridate $\alpha$-Li$_2$IrO$_3$. https://doi.org/10.1103/physrevb.99.235116

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