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arXiv 1402.0434cond-mat.mtrl-sci
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PrFe3(BO3)4:4f晶体场能级中非简并声子模在TO和LO声子频率之间的分裂

Splitting of a nondegenerate phonon mode in PrFe3(BO3)4: 4f crystal-field level between TO and LO phonon frequencies

K. N. Boldyrev, T. N. Stanislavchuk, A. A. Sirenko, L. N. Bezmaternykh, M. N. Popova

摘要:

在多铁性PrFe_3(BO_3)_4的远红外光谱中观察到了一种新的晶体场激发声子耦合效应。对应于50 cm-1(1.5 THz)附近的A2对称非简并声子模的剩余辐射带在100 K左右分裂成两个带,远高于TN = 32 K。随着温度的进一步降低,这些谱带逐渐移动和变窄,在TN处表现出明显的特性。所观察到的效应被解释为A2声子模式与Pr 3+的4f晶体场电子激发的相互作用,Pr 3+的频率落入声子模式的TO-LO频率区域。反转的TO和LO频率的电子激发和耦合的电子-声子模式的形成进行了讨论。用理论曲线拟合TO频率与温度的实验曲线,得到电子-声子耦合常数为14.6 cm-1。

英文摘要:

A new effect originating from the crystal-field-excitation - phonon coupling was observed (in the far infrared spectra of a multiferroic PrFe3(BO3)4). The reststrahlen band corresponding to the A2 symmetry nondegenerate phonon mode near 50 cm-1 (1.5 THz) splits into two bands at about 100 K, well above TN = 32 K. These bands shift and narrow progressively with further lowering the temperature, demonstrating pronounced peculiarities at TN. The observed effects were explained by an interaction of the A2 phonon mode with the 4f crystal-field electronic excitation of Pr3+ whose frequency falls into the TO - LO frequency region of the phonon mode. Inversion of the TO and LO frequencies for the electronic excitation and a formation of coupled electron-phonon modes are discussed. Fitting of the TO frequency vs temperature experimental plots by theoretical curves revealed the value 14.6 cm-1 for the electron-phonon coupling constant.

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