Possible Polaron Effect in Complex Terahertz Conductivity of Electron-Doped Nanoporous Crystal 12CaO・7Al_2O_3(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We have measured the temperature dependence of the complex THz conductivity σ(ω) of electrondoped 12CaO・7Al_2O_3 (C12A7) (carrier concentration, 5×10^<18> cm^<-3>) showing the DC conductivity of Mott variable-range hopping. The complex dielectric constant of electron-doped C12A7 gradually decreases to that of undoped C12A7 with decreasing temperature, which is caused by the freeze-out of hopping carriers. The extracted σ(ω) stemming from the electrons was found to obey the Jonscher law between 0.3 and 1.2THz in the measured temperature range, 50-300K. Detailed discussions are presented by employing several pair-approximation models generally describing the frequency and temperature dependences of the power s in the Jonscher law up to GHz range, from which it has been revealed that the most plausible model is one taking into account a polaron effect. A distribution of relaxation time conjectured from the model is presented. Our results significantly suggest the extension of the use of the Jonscher law and the pair-approximation model beyond the GHz range, although some modifications may be needed for the latter.
社団法人日本物理学会の論文
2006-08-15