从2 K到1700 K太赫兹到中红外的h-ErMnO3吸收率、反射率和发射率：载流子屏蔽、弗罗希共振、小极化子和双极化子
h-ErMnO3 absorbance, reflectivity and, emissivity in the THz to mid-infrared from 2 K to 1700 K: carrier screening, Fröhlich resonance, small polarons, and bipolarons
摘要：
我们报道了温度依赖的太赫兹到中红外响应的六角ErMnO 3的吸收，反射率和发射率技术从2 K到1700 K。在低温下，最低频率的振动模式共存的顺磁激发与定义良好的晶体场稀土纯磁性副本在一个有趣的声子磁收敛。随着温度的升高，一些接近空间群的振动带发生了展宽和软化。特别是，在288-329 cm-1（300 K）范围内的一组独特的带具有其轮廓被载波屏蔽的分量，该分量在~830 K和~1500 K之间的中间阶段变得几乎完全模糊。低于TC ~830 K，该不对称带进一步分裂为自旋声子相互作用和三倍的晶胞发生揭示了一个微妙的平衡的长，短距离相互作用。环境拉曼散射带来了一个Fröhlich共振由于库仑之间的相互作用载流子和纵向光学声子模式的宏观领域的证据。我们发现它是动态相关的六边形c轴负热膨胀。中红外（MIR）光学电导率表明，在高温下，小极化子和双极化子也起作用，在1600 K时，低频Drude贡献由电子跳跃触发，表明绝缘体-金属相变，而MIR响应表明单个小极化子和双极化子共存。我们画了一个平行的不适当的铁电体维持晶格无公度中间相和单位晶胞三倍。我们认为，在h-RMnO 3（R=稀土，Y）的化合物家族的中间相被认为是不相称的TINC ~1500 K和铁电锁定在TC ~830 K界定这一制度在h-ErMnO 3。
英文摘要：
We report the temperature dependent THz to mid-infrared response of hexagonal-ErMnO3 using absorption, reflectivity, and emissivity techniques from 2 K to 1700 K. At low temperatures, lowest frequency vibrational modes coexist with paramagnon excitations associated with well-defined crystal field Rare Earth pure magnetic replicas in an intriguing phonon-magnetic convergence. Increasing the temperature, a number of vibrational bands close to the space group predicted undergo profile broadening and softening. In particular, a distinctive set of bands in the 288-329 cm-1 (300 K) range has a component whose profile is carrier screened becoming nearly fully blurred in the intermediate phase between ~830 K and ~1500 K. Below TC ~830 K this asymmetric band further splits as spin phonon interaction and the tripling of the unit cell takes place revealing a delicate balance of long- and short-range interactions. Ambient Raman scattering brings up evidence of a Fröhlich resonance due to Coulomb interactions between carriers and the macroscopic field of the longitudinal optical phonon mode. We found it is dynamically correlated to the hexagonal c-axis negative thermal expansion. Mid-infrared (MIR) optical conductivity show that also plays a role in small polarons and mediates in high temperature bipolarones.At higher temperatures a low frequency Drude contribution is triggered by electron hopping signaling an insulator-metal phase transition at ~1600 K while the MIR response suggests coexistence between single small polarons and bipolarons. We draw a parallel with improper ferroelectrics sustaining a lattice incommensurate intermediate phase and unit cell tripling. We argue that in the h-RMnO3 (R=Rare Earth, Y) family of compounds the intermediate phase be considered incommensurate with onset at TINC ~1500 K and ferroelectric lock-in at TC ~830 K delimiting this regime in h-ErMnO3.
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