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arXiv · 1803.04056

Pressure-driven collapse of the relativistic electronic ground state in a honeycomb iridate

J. P. Clancy·H. Gretarsson·J. A. Sears·Yogesh Singh·S. Desgreniers·Kavita Mehlawat·Samar Layek·Gregory Kh. Rozenberg·Yang Ding·M. H. Upton·D. Casa·N. Chen·Junhyuck Im·Yongjae Lee·R. Yadav·L. Hozoi·D. Efremov·J. van den Brink·Young-June Kim
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Abstract

The electronic ground state in many iridate materials is described by a complex wave-function in which spin and orbital angular momenta are entangled due to relativistic spin-orbit coupling (SOC). Such a localized electronic state carries an effective total angular momentum of $J_{eff}=1/2$. In materials with an edge-sharing octahedral crystal structure, such as the honeycomb iridates Li2IrO3 and Na2IrO3, these $J_{eff}=1/2$ moments are expected to be coupled through a special bond-dependent magnetic interaction, which is a necessary condition for the realization of a Kitaev quantum spin liquid. However, this relativistic electron picture is challenged by an alternate description, in which itinerant electrons are confined to a benzene-like hexagon, keeping the system insulating despite the delocalized nature of the electrons. In this quasi-molecular orbital (QMO) picture, the honeycomb iridates are an unlikely choice for a Kitaev spin liquid. Here we show that the honeycomb iridate Li2IrO3 is best described by a $J_{eff}=1/2$ state at ambient pressure, but crosses over into a QMO state under the application of small (~ 0.1 GPa) hydrostatic pressure. This result illustrates that the physics of iridates is extremely rich due to a delicate balance between electronic bandwidth, spin-orbit coupling, crystal field, and electron correlation.

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J. P. Clancy, H. Gretarsson, J. A. Sears, Yogesh Singh, S. Desgreniers, Kavita Mehlawat, Samar Layek, Gregory Kh. Rozenberg, Yang Ding, M. H. Upton, D. Casa, N. Chen, Junhyuck Im, Yongjae Lee, R. Yadav, L. Hozoi, D. Efremov, J. van den Brink, Young-June Kim. 2018-03-11. Pressure-driven collapse of the relativistic electronic ground state in a honeycomb iridate. https://doi.org/10.1038/s41535-018-0109-0

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