Dependence of optical conductivity with δ in La2NiO4+δ single crystals

Optical conductivity and electrical resistivity of La2NiO4+δ ( δ = 0.11 and 0.14) single crystals have been investigated for the ( a , b ) plane. Results show several changes of regime that are connected with the onset of spin and charge order, static or dynamic. A surprising contrast of data for both samples, in optical and electrical conductivity, is observed at lowest temperatures. In particular, a pronounced spin glass behavior is observed for δ = 0.11 . In the δ = 0.14 sample, the progressive melting of the charge order scales with the temperature dependence of the oscillator strength of a “forbidden” mode related to folding to the Brillouin zone center of a mode for a wavevector q = ( 0.28 , 0.28 , 0 ) associated with the modulation of stripes.