Evolution of Superconductivity in BiS2-Based Superconductor LaO0.5F0.5Bi(S1−xSex)2

Hiroi, Takafumi; Kajitani, Joe; Omachi, Atsushi; Miura, Osuke; Mizuguchi, Yoshikazu

doi:10.7566/jpsj.84.024723

Cited by 57 publications

(60 citation statements)

References 35 publications

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“…Compressing in-plane Bi-S distance enhances Bi-S orbital overlaps, and bulk superconductivity emerges. Similar chemical pressure effect can be produced by Se substitution for the S site, as demonstrated in LaO0.5F0.5BiS2-ySey and Eu0.5La0.5FBiS2-ySey [23,24]. Although Bi-Ch plane expands by the substitution of in-plane S 2-by larger Se 2- [25], the packing density of Bi-Ch plane is enhanced due to the almost fixed structure (volume) of the LaO blocking layer [21].…”

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confidence: 52%

Intrinsic Phase Diagram of Superconductivity in the BiCh₂-Based System Without In-Plane Disorder

et al. 2017

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We have investigated the crystal structure and physical properties of LaO1-xFxBiSSe to reveal the intrinsic superconductivity phase diagram of the BiCh2-based layered compound family. From synchrotron X-ray diffraction and Rietveld refinements with anisotropic displacement parameters, we clearly found that the in-plane disorder in the BiSSe layer was fully suppressed for all x. In LaO1-xFxBiSSe, metallic conductivity and superconductivity are suddenly induced by electron doping even at x = 0.05 and 0.1 with a monoclinic structure. In addition, x (F concentration) dependence of the transition temperature (Tc) for x = 0.2-0.5 with a tetragonal structure shows an anomalously flat phase diagram. With these experimental facts, we have proposed the intrinsic phase diagram of the ideal BiCh2-based superconductors with less in-plane disorder.Since the discovery of Bi4O4S3 and REO1-xFxBiS2 (RE: rare earth) superconductors, BiCh2-based (Ch: chalcogen) superconductors have been drawing much attention as a new class of layered superconductors [1][2][3]. Since the crystal structure composed of alternate stacks of the electrically conducting BiCh2 layers and the insulating (blocking) layers resembles those of the Cuprate and the FeAs-based high-transition-temperature (high-Tc) superconductors [4,5], many experimental and theoretical studies have been performed to clarify the superconductivity mechanisms of this system and to increase Tc. However, the mechanisms have not been understood completely. Recently, Morice et al. proposed that a 2 weak-coupling electron-phonon mechanism cannot explain the emerging Tc, as high as 11 K, in the BiCh2-based systems, from first principle calculations [6]. Therefore, full understandings of the basic characteristics of the superconductivity in the BiCh2-based system are crucial.The parent phase of the BiCh2-based superconductor is a band insulator [1,7,8]. On the basis of the calculated band structure, electrons carriers are doped into the bands mainly composed of Bi-6px and Bi-6py components. Electron-doped BiCh2-based compounds are expected to become metallic. Indeed, superconductivity is experimentally observed in electron-doped compounds [1][2][3]. However, the real situations are not simple as expected from the band structure. Although the superconductivity in BiCh2-based compounds is emerged by carrier doping, metallic transport is sometimes absent, and weakly localized behavior (semiconducting-like behavior) is observed in electrical resistivity measurements; a good example would be optimally doped LaO0.5F0.5BiS2. In semiconducting-like samples of LaO0.5F0.5BiS2, bulk superconductivity is not observed, while weak (filamentary) superconductivity is observed. To induce bulk superconductivity in the LaO0.5F0.5BiS2 system, external pressure effects [9][10][11][12][13][14][15][16] and/or element substitution at the La site [17][18][19][20], which optimize the crystal structure, are available. Namely, both electron carrier doping and crystal structure optimization are required for the e...

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confidence: 52%

Intrinsic Phase Diagram of Superconductivity in the BiCh₂-Based System Without In-Plane Disorder

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“…In LaO0.5F0.5BiS2-xSex, the substitutions of Se for the S sites induces bulk superconductivity with a Tc of ~3.8 K [19,20]. Another isovalent substitution is the RE site substitution.…”

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confidence: 99%

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

et al. 2018

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In order to understand the mechanisms behind the emergence of superconductivity by the chemical pressure effect in REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd), where bulk superconductivity is induced by the substitutions with a smaller-radius RE, we performed synchrotron powder X-ray diffraction, and analyzed the crystal structure and anisotropic displacement parameters. With the decrease of the RE 3+ ionic radius, the in-plane disorder of the S1 sites significantly decreased, very similar to the trend observed in the Se-substituted systems: LaO0.5F0.5BiS2-xSex and Eu0.5La0.5FBiS2-xSex. Therefore, the emergence of bulk superconductivity upon the suppression of the in-plane disorder at the chalcogen sites is a universal scenario for the BiCh2-based superconductors. In addition, we indicated that the amplitude of vibration along the c-axis of the in-plane chalcogen sites may be related to the Tc in the BiCh2-based superconductors. . In addition, the observed temperature dependence of the electrical resistivity was not metallic-like; it showed a weakly localized behavior in LaO1-xFxBiS2, although band calculations suggested that the electron-doped LaO1-xFxBiS2 should be metal [4,5,12]. These results suggested that the doped electrons were localized by the effect of structural disorder.In order to induce bulk superconductivity in LaO1-xFxBiS2, high pressure effects can be employed.The application of an external pressure induces bulk superconductivity with a Tc of ~10 K [13][14][15]. In addition, samples annealed under a high pressure (~2 GPa) also exhibit bulk superconductivity with aTc of ~10 K [2,[16][17][18]. The emergence of bulk superconductivity and increase of Tc in the highpressure phase can be attributed to the structural phase transition from the tetragonal low-Tc phase to the monoclinic high-Tc phase [13].Another approach to induce bulk superconductivity in the LaO1-xFxBiS2 system is to introduce a chemical pressure by an isovalent substitution, such as Ch (Ch: S, Se) and/or RE site substitutions. In LaO0.5F0.5BiS2-xSex, the substitutions of Se for the S sites induces bulk superconductivity with a Tc of ~3.8 K [19,20]. Another isovalent substitution is the RE site substitution. With the decrease of the RE 3+ (mean) ionic radius in REO0.5F0.5BiS2, the BiS2 layer becomes compressed, in particular along the ab-plane direction, and bulk superconductivity is induced [21]. As the isovalent substitution does not significantly affect the carrier concentration, the structural optimization induces superconductivity in the Ch-and RE-substituted systems. In order to analyze the essential factor for the emergence of the superconductivity, we considered the commonality of the chemical pressure effects between the Ch-and RE substitutions, by introducing the concept of an in-plane chemical pressure [22].The emergence of the bulk superconductivity in the LaO0.5F0.5BiS2-xSex system was explained by the decrease in the in-plane disorder of the chalcogen sites with the increase of the Se content, which was detected thro...

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“…The filamentary superconductivity is suppressed by the small doping of Se, and bulk superconductivity is induced at x ≥ 0.4. T c increases with the increasing Se concentration [38]. 2017, 2, 6 6 of 10 the chemical pressure effect by the Se substitution seems to be the opposite to that by the substitution of the smaller RE 3+ .…”

Section: Chemical Pressure Effectmentioning

confidence: 91%

“…The filamentary superconductivity is suppressed by the small doping of Se, and bulk superconductivity is induced at x ≥ 0.4. Tc increases with the increasing Se concentration [38]. …”

Section: Chemical Pressure Effectmentioning

confidence: 91%

Discovery of BiS2-Based Superconductor and Material Design Concept

Mizuguchi

2017

Condensed Matter

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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.

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Evolution of Superconductivity in BiS₂-Based Superconductor LaO_0.5F_0.5Bi(S₁₋_xSe_x)₂

Abstract: We have systematically investigated the crystal structure, magnetic susceptibility, and electrical resistivity of the BiS 2 -based superconductor

Cited by 57 publications

References 35 publications

Intrinsic Phase Diagram of Superconductivity in the BiCh₂-Based System Without In-Plane Disorder

Intrinsic Phase Diagram of Superconductivity in the BiCh₂-Based System Without In-Plane Disorder

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

Discovery of BiS2-Based Superconductor and Material Design Concept

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Evolution of Superconductivity in BiS2-Based Superconductor LaO0.5F0.5Bi(S1−xSex)2

Abstract: We have systematically investigated the crystal structure, magnetic susceptibility, and electrical resistivity of the BiS 2 -based superconductor

Cited by 57 publications

References 35 publications

Intrinsic Phase Diagram of Superconductivity in the BiCh2-Based System Without In-Plane Disorder

Intrinsic Phase Diagram of Superconductivity in the BiCh2-Based System Without In-Plane Disorder

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS2-Based REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd)

Discovery of BiS2-Based Superconductor and Material Design Concept

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Evolution of Superconductivity in BiS₂-Based Superconductor LaO_0.5F_0.5Bi(S₁₋_xSe_x)₂

Intrinsic Phase Diagram of Superconductivity in the BiCh₂-Based System Without In-Plane Disorder

Intrinsic Phase Diagram of Superconductivity in the BiCh₂-Based System Without In-Plane Disorder

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)