Emergent Phenomena at Extreme Conditions in Spin-Orbit Coupled Pyrochlore Iridates

• Applicant: Dr. Harish Kumar
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 495076551

Interest in the pyrochlore iridates A2Ir2O7 has been blossoming in recent years in response to the theoretical and experimental realization of exotic and novel topological phases (Weyl semimetal and axion insulator) and quantum criticality. The f-d exchange interaction between A- and Ir-cations, which is considered to be a crucial ingredient for many topological phases in pyrochlore iridates, can be tuned by external pressure as well as chemical pressure (A-site substitution). The materials Pr2Ir2O7, Sm2Ir2O7 and Y2Ir2O7 are interesting members of this compound family containing A3+ (Pr3+:4f2, Sm3+:4f5 and Y3+:3d0) and Ir4+ (5d5) ions, where the A-site cation (different ionic size) determines the physical properties from complex metallic to magnetic insulating phases. Within this project, the materials Pr2Ir2O7, Sm2Ir2O7 and Y2Ir2O7 will be synthesized in the form of single crystals by the flux method. To experimentally realize the theoretically proposed novel topological phases, I will investigate the structural, optical and magnetic properties under extreme conditions, such as high pressure and low temperature, as well as under chemical pressure. For the characterization of the optical properties, infrared and Raman spectroscopy measurements will be performed. Firstly, the parent compounds will be characterized at ambient and high pressures. Secondly, I will tune the strength of f-d exchange interaction in Pr2Ir2O7 through doping at the A-site by Sm and Y, without affecting the spin-orbit coupling and electronic correlation strength. Then my focus will be to study the combined effect of chemical and hydrostatic pressures in (Pr1-xYx)2Ir2O7 and (Pr1-xSmx)2Ir2O7. Finally, the possible role of the f-d interaction for the magnetism in correlation with topological electronic phases will be explored.

• DFG Programme: Research Grants