Discovery of BiS2-Based Superconductor and Material Design Concept

Abstract

Abstract:In 2012, we discovered new layered superconductors whose superconducting states emerge in the BiS 2 layers. Since their crystal structure, composed of alternate stacks of BiS 2 conduction layers and electrically insulating (blocking) layers, is similar to those of cuprate and Fe-based superconductors, many researchers have explored new BiS 2 -based superconductors and have studied the physical and chemical properties of the BiS 2 -based superconductors. In this paper, we present the histories of the discovery of the first BiS 2 -based superconductor, Bi 4 O 4 S 3 , and the second one, LaO 1−x F x BiS 2 . The structural variation of the BiS 2 -based superconductor family is briefly introduced. Then, we show the material design concept for the emergence of bulk superconductivity in BiS 2 -based compounds. At the end, a possible strategy for the enhancement of the transition temperature in the BiS 2 -based superconductors is proposed. . Those layered superconductors have a layered structure composed of alternate stacks of conducting (superconducting) and insulating (blocking) layers. The FeAs layer and CuO 2 plane are the essential structures for the emergence of superconductivity in Fe-based and cuprate superconductors, respectively. Namely, by utilizing the structural flexibility, new superconductors with various stacking structures could be designed by changing the blocking layer and/or the thickness of the superconducting planes. Therefore, I aimed to discover a new layered superconductor with a new type of superconducting layer other than the FeAs layer and CuO 2 plane.To discover new layered superconductors, experience in the material design of the Fe-based superconductor family is very useful. A typical crystal structure of the Fe-based superconductor is the ZrSiCuAs-type (P4/nmm) structure, for example LaOFeAs [1]. As shown in Figure 1a, the crystal structure of LaOFeAs is composed of the FeAs superconducting layer and the LaO blocking layer. Among layered compounds, the ZrSiCuAs-type structure is one of the typical structures. For example, BiOCuSe, whose structure is composed of a CuSe conducting layer and a BiO blocking layer, is a famous thermoelectric material [4]. When substituting the CuSe layer of BiOCuSe with a CuS layer, we obtain BiOCuS with the ZrSiCuAs-type structure.

Theoretical study of fluorine doping in layered LaOBiS2 -type compounds

“…LaOBiS 2 , 1 which comprises blocking LaO layers and conducting BiS 2 layers, has attracted much attention as superconducting [2][3][4][5][6][7][8][9][10] and thermoelectric [11][12][13][14][15][16][17][18] material. One of the remarkable features of this material is a relatively low thermal conductivity, ~2 W m -1 K -1 at room temperature, 19 which is advantageous for increasing ZT.…”

Pressure-induced insulator to metal transition of mixed valence compound Ce(O,F)SbS2

“…These compounds have a layered structure that is composed of conducting layers (BiS2) and charge reservoir blocking layers. We can modify the combination of various conducting layers and blocking layers flexibly depending on a desired functionality in the material [7].…”

Layered Superconductors

“…Since new superconductors can be designed by replacing the structure of the blocking layers, such a layered superconductor system is a good playground for novel superconductivity with low dimensionality. In the paper by Mizuguchi, review of the discovery of the BiS 2 -based superconductor and material design concept is introduced [17]. In addition, original work on the single crystal growth and superconducting properties of antimony substituted NdO 0.7 F 0.3 BiS 2 is reported by Demura et al [18] Layered materials have been revisited due to the discovery of topological insulators and related superconductors.…”