High-energy electronic excitations in Sr$_2$IrO$_4$ observed by Raman scattering

TL;DR

This study uses Raman spectroscopy to identify high-energy electronic excitations in Sr$_2$IrO$_4$, revealing temperature and doping effects on these excitations and clarifying their electronic transition origins.

Contribution

It reports the observation of specific high-energy excitations in Sr$_2$IrO$_4$ and analyzes their temperature dependence and doping effects, providing new insights into the electronic structure.

Findings

Identified two high-energy excitations at 690 meV and 680 meV with different symmetries.

Observed peak narrowing and energy shifts with decreasing temperature.

Doping with Rh softens the $A_{1g}$ peak by 10% without affecting the $B_{1g}$ peak.

Abstract

Spin-orbit interaction in Sr$_2$IrO$_4$ leads to the realization of the $J_{\mathrm{eff}}$ = 1/2 state and also induces an insulating behavior. Using large-shift Raman spectroscopy, we found two high-energy excitations of the d-shell multipletat at 690 meV and 680 meV with $A_{1g}$ and $B_{1g}$ symmetry respectively. As temperature decreases, the $A_{1g}$ and $B_{1g}$ peaks narrow, and the $A_{1g}$ peak shifts to higher energy while the energy of the $B_{1g}$ peak remains the same. When 25$\%$ of Ir is substituted with Rh the $A_{1g}$ peak softens by 10$\%$ but the $B_{1g}$ peak does not. We show that both pseudospin-flip and non-pseudosin-flip dd electronic transitions are Raman active, but only the latter are observed.