Pressure-induced dimerization and crossover from negative to positive magnetoresistance in Ag₃LiIr₂O₆

Quantum spin liquid states have garnered significant attention as potential precursors for high-temperature superconductors. Researchers are aiming to achieve high-temperature superconductivity through regulation. However, previous studies have indicated that candidate materials with honeycomb structures, such as Na2IrO3 and alpha-Li2IrO3, remain in a magnetically ordered and insulating state. Pressure serves as an effective regulatory tool by adjusting atomic interactions through interatomic spacing manipulation, thereby influencing the band structure near the Fermi surface and consequently tuning quantum-state evolution. In this study, interlayer Li were substituted by Ag atoms in alpha-Li2IrO3 to obtain the Ag3LiIr2O6, and its transitions in structure and physical properties as functions of temperature and pressure were investigated. It has been observed that Ag3LiIr2O6 remains stable between -190 and 300(degrees)C without undergoing any structural phase transitions. High-pressure phase transitions occur at 3.0-7.5 and 12.0-16.1 GPa. The first structural phase transition, as deduced from high-pressure x-ray diffraction and Raman spectroscopy, is associated with Ir-Ir dimerization and IrO6 octahedral distortion. Corresponding resistance measurements indicate a decreasing rate reduction in resistance near 5.2 GPa due to dimerization. Further compression leads to the existence of a minimum room-temperature resistance at similar to 19.5 GPa. A transition from negative to positive magnetoresistance occurs at 12.4 GPa under 2 K. Further analysis suggests that the transition from negative to positive magnetoresistance may be connected to the valence change of Ag from +1 to 0. Although the desired insulator-to-metal transition was not achieved, we have explored the correlation between structural and physical property transitions under high pressure, laying the groundwork for future investigations.