Optical study of the orbital ordered state inLa4Ru2O10

Abstract

We present the optical study of the ruthenateLa4Ru2O10, which undergoes a semiconductor–semiconductor transition at 160 K. Two Ru–Ruinterband transition peaks can be found in its HT phase. When temperaturedecreases across the transition, a transfer of spectral weight from low to highenergy occurs. The peak which is located at lower energy in the HT phase isstrongly suppressed below 160 K. Based on the analysis of structural distortionsassociated with this transition, we show that the spectral changes can be wellunderstood by considering energetically reasonable orbital-selective occupancies of Rut2g electrons. This proposed order of orbital energies offers specific insights into the HTinsulating behavior, while the LT picture supports the current picture of a spin-singletground state.