Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I3
Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I3
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电荷排序相的电动力学响应：α-(BEDT-TTF)2I3 的介电和光学研究
DOI：
10.1103/physrevb.83.165128
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发表时间：
2010
影响因子：
3.7
通讯作者：
M. Dressel
中科院分区：
文献类型：
--
作者：
T. Ivek;B. Korin;O. Milat;S. Tomi'c;C. Clauss;N. Drichko;D. Schweitzer;M. Dressel
我们报告的各向异性响应，电荷和晶格动力学的正常和电荷有序相与水平条纹在单晶的有机导体α-（BEDT-TTF）2 I3直流电阻率，介电和光谱测定。过阻尼Drude响应和小的电导率各向异性光学观察到的是一致的弱温度依赖性的直流电导率和各向异性在高温下。分子振动nu 27（Bu）的分裂证明了在TCO=136 K以下静电荷序的突然出现。在晶体的ab平面内测量的光学电导率的下降的特征在于由各向同性的间隙，该间隙打开约75 meV，其中几个声子变得明显低于。相反，直流电导率各向异性急剧上升，在50 K时达到比高温时大25倍的值。在该平面内的介电响应显示出两个宽弛豫模式，其强度Δ LD ~= 5000和Δ SD ~= 400，中心在1 kHz < f_LD < 100 MHz和f_SD ~= 1 MHz。大模（LD）的平均弛豫时间的各向异性密切遵循各自的直流电导率比的温度行为。我们认为，这种类相子激发最好描述为一个2kF键电荷密度波理论上预期分层四分之一填充的电子系统与水平条纹的长波长激发。相反，基于理论上预期的电荷有序相的铁电性质，我们关联的小模式（SD）松弛与畴壁对的运动，创建在两种类型的域之间的接口，沿着的a和B轴。我们还考虑了其他可能的理论解释，并讨论其局限性。
We report on the anisotropic response, the charge and lattice dynamics of normal and charge-ordered phases with horizontal stripes in single crystals of the organic conductor alpha-(BEDT-TTF)2I3 determined by dc resistivity, dielectric and optical spectroscopy. An overdamped Drude response and a small conductivity anisotropy observed in optics is consistent with a weakly temperature dependent dc conductivity and anisotropy at high temperatures. The splitting of the molecular vibrations nu27(Bu) evidences the abrupt onset of static charge order below TCO=136 K. The drop of optical conductivity measured within the ab plane of the crystal is characterized by an isotropic gap that opens of approximately 75 meV with several phonons becoming pronounced below. Conversely, the dc conductivity anisotropy rises steeply, attaining at 50 K a value 25 times larger than at high temperatures. The dielectric response within this plane reveals two broad relaxation modes of strength Deltaepsilon_LD ~= 5000 and Deltaepsilon_SD ~= 400, centered at 1 kHz < f_LD < 100 MHz and f_SD ~= 1 MHz. The anisotropy of the large-mode (LD) mean relaxation time closely follows the temperature behavior of the respective dc conductivity ratio. We argue that this phason-like excitation is best described as a long-wavelength excitation of a 2kF bond-charge density wave expected theoretically for layered quarter-filled electronic systems with horizontal stripes. Conversely, based on the theoretically expected ferroelectric-like nature of the charge-ordered phase, we associate the small-mode (SD) relaxation with the motion of domain-wall pairs, created at the interface between two types of domains, along the a and b axes. We also consider other possible theoretical interpretations and discuss their limitations.