Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
1] Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany [2] Institute of Applied Physics, Academy of Sciences of Moldova, 2028 Chisinau, Republic of Moldova.
Nat Commun. 2014;5:3202. doi: 10.1038/ncomms4202.
Understanding the origin of high-temperature superconductivity in copper- and iron-based materials is one of the outstanding tasks of current research in condensed matter physics. Even the normal metallic state of these materials exhibits unusual properties. Here we report on a hierarchy of temperatures T(c)<T(gap)<T(met) in superconducting Rb(1-x)Fe(2-y)Se(2) observed by THz spectroscopy (T(c)=critical temperature of the superconducting phase; T(gap)=temperature below which an excitation gap opens; T(met)=temperature below which a metallic optical response occurs). Above T(met)=90 K the material reveals semiconducting characteristics. Below T(met) a coherent metallic THz response emerges. This metal-to-insulator-type, orbital-selective transition is indicated by an isosbestic point in the temperature dependence of the optical conductivity and dielectric constant at THz frequencies. At T(gap)= 61 K, a gap opens in the THz regime and then the superconducting transition occurs at T(c)=32 K. This sequence of temperatures seems to reflect a corresponding hierarchy of the electronic correlations in different bands.
理解铜基和铁基高温超导材料的起源是凝聚态物理当前研究的杰出任务之一。即使是这些材料的正常金属态也表现出异常的性质。在这里，我们通过太赫兹光谱学报告了超导 Rb(1-x)Fe(2-y)Se(2)中观察到的温度 T(c)<T(gap)<T(met)的层次结构（T(c)=超导相的临界温度；T(gap)=激发能隙打开以下的温度；T(met)=发生金属光学响应以下的温度）。在 T(met)=90 K 以上，材料呈现半导体特性。在 T(met)以下，出现相干的金属太赫兹响应。这种金属-绝缘体型、轨道选择性的转变由太赫兹频率下光学电导率和介电常数的温度依赖性中的等色点指示。在 T(gap)=61 K 时，太赫兹区域出现能隙，然后在 T(c)=32 K 时发生超导转变。这些温度的顺序似乎反映了不同能带中电子相关的相应层次结构。
