Compressive-strain induced enhancement of exchange interactions and short-range magnetic order in Sr$_2$IrO$_4$ investigated by Raman spectroscopy (1908.02716v1)

Abstract: We have carried out Raman spectroscopy experiments to investigate two-magnon excitations in epitaxial thin films of the quasi-two-dimensional antiferromagnetic Mott insulator Sr$2$IrO$_4$ under in-plane misfit strain. With in-plane biaxial compression, the energy of the two-magnon peak increases, and the peak remains observable over a wider temperature range above the N\'eel temperature, indicating strain-induced enhancement of the superexchange interactions between $\it{J}{eff}$ = 1/2 pseudospins. From density functional theory calculations, we have found an increase of the nearest-neighbor hopping parameter and exchange interaction with increasing biaxial compressive strain, in agreement with the experimental observations. Our experimental and theoretical results provide perspectives for systematic, theory-guided strain control of the primary exchange interactions in 5$\it{d}$ transition metal oxides.