Structural Difference in Superconductive and Nonsuperconductive Bi-S Planes within Bi4O4Bi2S4 Blocks

Discovery of a Superconductor Bi5 O4 S3 Cl Containing the Unique BiS3 Layer

The BiS2 -based layered superconductors with structures similar to those of cuprates and iron-based superconductors have stimulated much research interest. Here, a new quaternary compound is reported, Bi5 O4 S3 Cl, which crystalizes in a tetragonal structure with P4/mmm (No. 123) space group having alternately stacking unique BiS3 layers and Bi2 O2 layers along the c-axis with a Cl atom located at the center of the unit cell. A superconducting transition above 3 K is observed for both electrical transport and magnetic measurements. Hall resistivity measurements show its multiband character with a conduction dominated by electron-like charge carriers. The first-principles calculations exhibit that the semiconducting parent phase Bi5 O4 S3 Cl becomes metallic when sulfur vacancies are introduced, which hints the origin of superconductivity in Bi5 O4 S3 Cl. The findings will inspire the exploration of new BiS-based superconductors.

Two-Dimensional Superconductivity in Air-Stable Single-Crystal Few-Layer Bi3O2S3

The progress of unconventional superconductors at the two-dimensional (2D) limit has inspired much interest. Recently, a new superconducting system was discovered in the semimetallic ternary Bi-O-S family. However, pure-phase crystals are difficult to synthesize because of the complicated stacking sequence of multiple charged layers and similar formation kinetics among ternary polytypes, leaving several fundamental issues regarding the structure-superconductivity correlation unresolved. Herein, 2D single-crystal ultrathin Bi3O2S3 nanosheets are prepared by using low-pressure chemical vapor deposition, and their atomic arrangement is clarified. Magnetotransport measurements indicate a superconducting transition at ∼6.1 K that is thickness-independent. The transport results demonstrate 2D superconducting characteristics, such as the Berezinskii-Kosterlitz-Thouless transition, and strong anisotropy with magnetic field orientations following the 2D Tinkham formula. The difference from superconductivity of powder is demonstrated from the perspective of their corresponding microstructures. These results corroborate the superconducting behavior of Bi3O2S3, providing fresh insights into the search for other bismuth oxychalcogenides and derivative BiS2-based analogues at the 2D limit.

Crystal Structure and Superconductivity of Tetragonal and Monoclinic Ce1- xPr xOBiS2

Ce_{1- x}Pr _xOBiS₂ powders and Ce_0.5Pr_0.5OBiS₂ single crystals were synthesized and their structure and superconductive properties were examined by X-ray diffraction, X-ray absorption, electronic resistivity, and magnetization. While PrOBiS₂ was found to be in a monoclinic phase with one-dimensional Bi-S zigzag chains showing no superconductive transition above 0.1 K, CeOBiS₂ was in a tetragonal phase with two-dimensional Bi-S planes showing zero resistivity below 1.3 K. In the range x = 0.3-0.9 in Ce_{1- x}Pr _xOBiS₂, both monoclinic and tetragonal phases were formed together with zero resistivity up to a maximum temperature of 2.2 K. A Ce_0.5Pr_0.5OBiS₂ single crystal, which showed both zero resistivity and a decrease in magnetization at ∼2.4 K, presented a tetragonal structure. Short Bi-S bonding in flat two-dimensional Bi-S planes and mixed Ce³⁺/Ce⁴⁺ were characteristic features of the Ce_0.5Pr_0.5OBiS₂ single crystal, which presumably triggered its superconductivity.