OPTICAL SPECTROSCOPY OF THE CHARGE-ORDERING TRANSITION IN LA1.67SR0.33NIO4

摘要: Optical spectra of a single crystal ${\mathrm{La}}_{1.67}$${\mathrm{Sr}}_{0.33}$${\mathrm{NiO}}_{4}$, which undergoes charge-ordering transition at ${\mathit{T}}_{\mathrm{CO}}$\ensuremath{\sim}240 K, have been investigated for wide ranges photon energy (0.008--3 eV) and temperature (10--480 K). The opening charge gap as well change the magnitude (2\ensuremath{\Delta}) with is clearly observed below ${\mathit{T}}_{\mathrm{CO}}$, an anomalously large ratio 2\ensuremath{\Delta}(T=0)/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathrm{CO}}$ (\ensuremath{\sim}13). Conspicuous spectral also above ${\mathit{T}}_{\mathrm{CO}}$ over region up to 2 eV, suggests persistent fluctuation ordering or formation small polarons ${\mathit{T}}_{\mathrm{CO}}$. \textcopyright{} 1996 American Physical Society.