Temperature-dependent optical conductivity of layered LaSrFeO4
Por:
Reul J., Fels L., Qureshi N., Shportko K., Braden M., Grüninger M.
Publicada:
1 ene 2013
Resumen:
Compounds with intermediate-size transition metals such as Fe or Mn are close to the transition between charge-transfer systems and Mott-Hubbard systems. We study the optical conductivity s(?) of insulating layered LaSrFeO4 in the energy range 0.5-5.5 eV from 15 K to 250 K by the use of spectroscopic ellipsometry in combination with transmittance measurements. A multipeak structure is observed in both sa(?) and sc(?). The layered structure gives rise to a pronounced anisotropy, thereby offering a means to disentangle Mott-Hubbard and charge-transfer absorption bands. We find strong evidence that the lowest dipole-allowed excitation in LaSrFeO4 is of Mott-Hubbard type. This rather unexpected result can be attributed to Fe 3d-O 2p hybridization and in particular to the layered structure with the associated splitting of the e g level. In general, Mott-Hubbard absorption bands may show a strong dependence on temperature. This is not the case in LaSrFeO4, in agreement with the fact that spin-spin and orbital-orbital correlations between nearest neighbors do not vary strongly below room temperature in this compound with a high-spin 3d5 configuration and a Néel temperature of T N=366 K. © 2013 American Physical Society.
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