The temperature dependence of the low-energy tail of the interband optical absorption band at the Peierls edge has been studied in halogen-bridged linear-chain complexes, [Pt(en)2][Pt(en)2Cl2](ClO4)4 and [Pt(en)2][Pt(en)2Cl2](BF4)4, en being ethylenediamine. The absorption spectrum and its temperature dependence are explained well in terms of the subgap density of states of the one-dimensional electronic bands induced by the quantum vibration of Cl ions of the breathing mode. Both substances are found to have a dimensionless electron-phonon coupling constant of λ≊1.2, the zero-temperature gap parameter of Δ0≊1.45 eV, and the transfer integral of t0≊0.4 eV. Because of the strong electron-phonon coupling the temperature dependence of the energy gap is dominated by the self-energy effect; even at 0 K the self-energy amounts to 0.07–0.08 eV, being considerably greater than the self-energies in usual semiconductors. The role of the anharmonicity of the chainlike Pt-Cl bonds is discussed in relation to the origin of the large gap parameter.
パイエルス端から低エネルギー側に裾を引く光吸収帯の温度依存性をClO4塩とBF4塩の2つの擬一次元PtCl錯体について調査した。実験結果は、Ptを架橋しているCl-イオンの量子振動がパイエルス端の低エネルギー側に裾を引くように電子の状態密度を誘起するという理論によってよく説明できることが分かった。実験データより電子・音子結合定数、エネルギーギャップ定数および移動積分が定量的に評価された。これらの値からさらに、擬一次元PtCl錯体特有のセルフエネルギー効果とPt-Cl結合の非調和性にまで踏み込んだ知見が得られた。
Subgap optical absorption induced by quantum lattice fluctuations at the Peierls edge in PtCl-chain complexes
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