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arXiv 2004.08819cond-mat.supr-con
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双层化合物RbCa $_2$ Fe PDMATHAAD As PDMATHAAD F $_2$的$c$轴响应中超导诱导的横向等离子体模和声子异常

Superconductivity-induced transverse plasma mode and phonon anomaly in the $c$-axis response of the bilayer compound RbCa$_2$Fe$_4$As$_4$F$_2$

B. Xu, D. Munzar, A. Dubroka, E. Sheveleva, F. Lyzwa, P. Marsik, C. N. Wang, Z. C. Wang, G. H. Cao, C. Bernhard

摘要:

用红外光谱研究了砷化铁超导体ACaPDMATHABMN FePDMATHABMO AsPDMATHABMO FPDMATHABMN(A = Rb,Cs)的面外($c$ -轴)响应,它具有类似于高$T_c$铜酸盐YBaPDMATHABMN CuPDMATHABMQ OPDMATHABMR(YBCO)和BiPDMATHABMN SrPDMATHABMN CaCuPDMATHABMN OPDMATHABMS(Bi 2212)的双层结构.在类似的铜氧化物,我们观察到超导诱导的横向等离子体模式(tPM)和声子异常,这两个签名的局部电场效应,产生的局部电导率之间的差异很大的内和间双层区域。使用多层模型开发的铜酸盐,我们得到了一个很好的描述$c$轴的响应,并推导出局部电导率在$T \simeq T_c$的$σ_1^{\mathrm{bl}}(ω\rightarrow 0) \simeq$ 11000 $Ω^{-1}\mathrm{cm}^{-1}$和$σ_1^{\mathrm{int}}(ω\rightarrow 0) \simeq$ 15 $Ω^{-1}\mathrm{cm}^{-1}$,分别,这是类似于以前发现的欠掺杂的YBCO。不同于铜酸盐,我们没有发现正常状态的赝隙的部分抑制的低能量的电子状态,设置在已经远远高于$T_c$的证据。在$T_c \simeq$ 30~K以上也没有明显的前兆超导配对关联开始的迹象。这突出了赝能隙和远高于$T_c$的前体超导配对是具有强电子相关性的铜酸盐的独特特征,例如,不仅仅是由于层状晶体结构引起的强各向异性电子响应的结果。

英文摘要:

With infrared spectroscopy we studied the out-of-plane ($c$-axis) response of the iron arsenide superconductor ACa$_2$Fe$_4$As$_4$F$_2$ (A = Rb,Cs) which has a bilayer structure similar to the high $T_c$ cuprates YBa$_2$Cu$_3$O$_7$ (YBCO) and Bi$_2$Sr$_2$CaCu$_2$O$_8$ (Bi2212). In analogy to the cuprates, we observe a superconductivity-induced transverse plasma mode (tPM) and a phonon anomaly that are both signatures of local electric field effects that arise from a large difference between the local conductivities in the intra- and inter-bilayer regions. Using a multilayer model developed for the cuprates, we obtain a good description of the $c$-axis response and derive the local conductivities at $T \simeq T_c$ of $σ_1^{\mathrm{bl}}(ω\rightarrow 0) \simeq$ 1\,000 $Ω^{-1}\mathrm{cm}^{-1}$ and $σ_1^{\mathrm{int}}(ω\rightarrow 0) \simeq$ 15 $Ω^{-1}\mathrm{cm}^{-1}$, respectively, that are similar to the ones previously found in underdoped YBCO. Different from the cuprates, we find no evidence of a normal state pseudogap in terms of a partial suppression of the low-energy electronic states that sets in already well above $T_c$. There is also no clear sign of an onset of precursor superconducting pairing correlations well above $T_c \simeq$ 30~K. This highlights that the pseudogap and the precursor superconducting pairing well above $T_c$ are unique features of the cuprates with their strong electronic correlations and, for example, not just the result of a strongly anisotropic electronic response due to the layered crystal structure.

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