Abstract
The similarities to cuprates make iridates an interesting potential platform for investigating superconductivity. Equally attractive are their puzzling complex intrinsic interactions. Here, we report an ultrafast optical spectroscopy investigation of a coherent phonon mode in , a bilayer Ruddlesden-Popper perovskite iridate. An anomaly in the optical phonon is unambiguously observed below the Néel temperature , which we attribute to pseudospin-lattice coupling (PLC). Significantly, we find that PLC is the dominant interaction at low temperature, and we directly measure the PLC coefficient to be , which is two orders of magnitude higher than that in manganites () and comparable to that in CuO (, the strongest PLC or spin-lattice coupling (SLC) previously known). Moreover, we find that the strong PLC induces an anisotropic negative thermal expansion. Our findings highlight the key role of PLC in iridates and uncovers another intriguing similarity to cuprates.
- Received 19 July 2018
DOI:https://doi.org/10.1103/PhysRevB.99.094307
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