Combined effects of strong spin-orbit coupling and electronic correlation make the 5d-transition metal oxide Sr₂IrO₄ a potentially interesting system, because it can host exotic states of matter due to its inherently strong spin-orbit coupling. The application of external pressure can tune the interatomic distance and atomic arrangements, leading to a tuning of spin-orbit interaction and consequently the electronic and magnetic ground states.

We have studied high pressure powder XRD of Sr₂IrO₄ up to 43 GPa at 20K using the XDS beamline at Brazilian Synchrotron Light Laboratory (LNLS). The tetragonal structure of Sr₂IrO₄ seems to be maintained in this pressure range, however, a couple of lattice anomalies are observed, reflecting crossovers between isostructural competing states. The c/a ratio is revealing that the unit-cell response to pressure is anisotropic. Up to 9 GPa, the c/a ratio is constant, above 15 GPa, the tetragonal cell elongates at a significantly higher rate, between 9 and 15 GPa, the c/a ratio increase moderately. This strikingly rich behavior is suggestive of a nontrivial lattice relaxation with increasing pressures, possibly as a response of electronic phase transitions. The linewidths of (004), (116), (200), and (220) diffraction peaks are also showing the anomalous behavior at ~ 9 and 15 GPa. We extend our experiment to do XRD measurements at fixed pressure (13.7±0.5 GPa) and as a function of temperature.     

Acknowledgment: FAPESP Grant Nos.: 2016/00756-6 and 2017/10581-1