Orbital-selective metal-insulator transition and gap formation above TC in superconducting Rb(1-x)Fe(2-y)Se2.
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.
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
Zhe
Z
Wang
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
M
M
Schmidt
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
J
J
Fischer
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.
V
V
Tsurkan
Theoretical Physics III, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
M
M
Greger
Theoretical Physics III, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
D
D
Vollhardt
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
A
A
Loidl
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
J
J
Deisenhofer