Pressure-induced anomalous insulating behavior in frustrated iridate La3Ir3O11 * *Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0305704 and 2016YFA0401804), the National Natural Science Foundation of China (Grant Nos. U1632275, U1932152, 11874362, 11704387, 11804344, 11804341, 11974016, U19A2093, and U1832209), the Natural Science Foundation of Anhui Province, China (Grant Nos. 1808085MA06, 2008085QA40, and 1908085QA18), the

Abstract

The geometrically frustrated iridate La3Ir3O11 with strong spin–orbit coupling and fractional valence was recently predicted to be a quantum spin liquid candidate at ambient conditions. Here, we systematically investigate the evolution of structural and electronic properties of La3Ir3O11 under high pressure. Electrical transport measurements reveal an abnormal insulating behavior rather than metallization above a critical pressure P c ∼ 38.7 GPa. Synchrotron x-ray diffraction (XRD) experiments indicate the stability of the pristine cubic KSbO3-type structure up to 73.1 GPa. Nevertheless, when the pressure gradually increases across P c, the bulk modulus gets enhanced and the pressure dependence of bond length d Ir – Ir undergoes a slope change. Consistent with the XRD data, detailed analyses of Raman spectra reveal an abnormal redshift of Raman mode and a change of Raman intensity around P c. Our results demonstrate that the pressure-induced insulating behavior in La3Ir3O11 can be assigned to the structural modification, such as the distortion of IrO6 octahedra. These findings will shed light on the emergent abnormal insulating behavior in other 5d iridates reported recently.