Evolution of the 251 cm-1 infrared phonon mode with temperature in Ba0.6K0.4Fe2As2

The far-infrared optical reflectivity of an optimally doped Ba1-xKxFe2As2(x =0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1 . This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound.     

Evolution of the 251 cm-1 temperature in infrared phonon mode with Ba0.6K0.4Fe2As2

The far-infrared optical reflectivity of an optimaUy doped Ba1-xKxFe2As2 （x = 0.4） single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 em-1. This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continu- ously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observa- tions indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Bao.6Ko.4Fe2As2 compound.     

La0.33Pr0.34Ca0.33MnO3薄膜的应变效应

采用脉冲激光沉积法分别在(100)LaAlO₃和(100)SrTiO₃基片上生长了La_0.33Pr_0.34Ca_0.33MnO₃薄膜,并通过磁测量和电输运测量对生长在不同基片上的La_0.33Pr_0.34Ca_0.33MnO₃薄膜的物性进行了研究.结果表明,基片和薄膜之间的压应力导致La_{关键词： 钙钛矿锰氧化物 相分离 电荷有序}     

In-plane optical spectral weight redistribution in the optimally doped Ba_(0.6)K_(0.4)Fe_2As_2 superconductor

We performed detailed temperature-dependent optical measurements on optimally doped Ba0.6K0.4Fe2As2 single crystal, We examine the changes of the in-plane optical conductivity spectral weight in the normal state and the evolution of the superconducting condensate in the superconducting state. In the normal state, the low-frequency spectral weight shows a metallic response with an arctan （T） dependence, indicating a T-linear scattering rate behavior for the carriers. A high energy spectral weight transfer associated with the Hund＇s coupling occurs from the low frequencies below 4000 cm^-1 5000 cm^-1 to higher frequencies up to at least 104 cm^-1. Its temperature dependence analysis suggests that the Hund＇s coupling strength is continuously enhanced as the temperature is reduced. In the superconducting state, the FGT sum rule is conserved according to the spectral weight estimation within the conduction bands, only about 40% of the conduction bands participates in the superconducting condensate indicating that Ba0.6K0.4Fe2As2 is in dirty limit.     

Evolution of the 251 cm^-1 infrared phonon mode with temperature in Ba_0.6K_0.4Fe₂As₂

The far-infrared optical reflectivity of an optimally doped Ba1-xKxFe2As2(x =0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1 . This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound.     

Temperature-dependent far-infrared properties of Bi12GeO20 single crystal

Far-infrared reflectivity spectra of bismuth germanium oxide (Bi12GeO20) single crystals are measured from room temperature down to 10 K. All the reflectivity spectra are fitted to a complex dielectric function ε(ω) in the factorised form. Phonon modes at low frequency are found to develop upon decreasing temperature and gain considerable spectrum weight below 150 K. The temperature-dependent static dielectric constants are obtained from the Lyddane-Sachs-Teller relation based on the obtained oscillator parameters. The dielectric constants are found to increase upon decreasing temperature, which is attributed to the charge transfer among the ions in the unit cell with the temperature varying.     

Magnetoresistivity and filamentary superconductivity in nickel-doped BaFe_2As_2

We present magnetotransport studies on a series of BaFe_(2-x)Ni_xAs_2(0.03 ≤ x ≤ 0.10) single crystals. In the underdoped(x = 0.03) non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity(FLSC). FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped(x = 0.10) compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.     

La0.33Pr0.34Ca0.33MnO3薄膜的应变效应

采用脉冲激光沉积法分别在(100)LaAlO3和(100)SrTiO3基片上生长了La0.33Pr0.34Ca0.33MnO3 薄膜,并通过磁测量和电输运测量对生长在不同基片上的La0.33Pr0.34Ca0.33MnO3薄膜的物性进行了研究.结果表明,基片和薄膜之间的压应力导致La0.33Pr0.34Ca0.33MnO3薄膜容易出现铁磁相,而电荷有序相则被抑制.基片和薄膜之间的张应力则导致La0.33Pr0.34Ca0.33MnO3薄膜容易出现电荷有序相,铁磁相被抑制.导致该现象的可能原因之一是应力使得晶格中Mn-O键角发生改变而引起双交换作用的改变.     

红外光谱在铁基超导材料研究中的应用

红外光谱作为一种体测量手段在非常规超导材料的研究中占有非常重要的地位。本文介绍傅立叶变换红外光谱的基本原理,用来测量固体材料绝对反射率的原位镀膜技术,数据分析中常用的方法和理论模型,以及如何利用该技术手段观测和研究铁基超导材料中的超导能隙,电子配对对称性,自旋密度波能隙,非费米液体行为,晶格振动模式,以及不同相之间的相互关系和不同激发之间的相互作用等超导研究中的重要问题。