Superconductivity in Layered Oxychalcogenide La₂O₂Bi₃AgS₆

Abstract

Recently, we reported the observation of superconductivity at ~0.5 K in a La2O2M4S6-type (M: metal) layered oxychalcogenide La2O2Bi3AgS6, which is a layered compound related to the BiS2-based superconductor system but possesses a thicker Bi3AgS6-type conducting layer. In this study, we have developed the La2O2Bi3AgS6-type materials by element substitutions to increase the transition temperature (Tc) and to induce bulk nature of superconductivity. A resistivity anomaly observed at 180 K in La2O2Bi3AgS6 was systematically suppressed by Sn substitution for the Ag site. By the Sn substitution, Tc increased, and the shielding volume fraction estimated from magnetization measurements also increased. The highest Tc (= 2.3 K) and the highest shielding volume fraction (~20%) was observed for La2O2Bi3Ag0.6Sn0.4S6. The superconducting properties were further improved by Se substitutions for the S site. By the combinational substitutions of Sn and Se, bulk-superconducting phase of La2O2Bi3Ag0.6Sn0.4S5.7Se0.3 with a Tc of 3.0 K (Tc onset = 3.6 K) was obtained.

Superconductivity in La2O2M4S6 -Type Bi-based Compounds: A Review on Element Substitution Effects

“…Later on, the metal (M) site of La 2 O 2 M 4 S 6 has been modified as M = Bi 3 Ag, and the resultant compound was La 2 O 2 Bi 3 AgS 6 [51] . This newly designed oxychalcogenide La 2 O 2 Bi 3 AgS 6 showed metallic conductivity and superconductivity at T c = 0.5 K [52]. Previous studies on the two-layer-type (BiS 2 -based LnO 1−x F x BiS 2 ) phase has suggested that the doping effect at the various sites of a compound induced bulk superconductivity or improve the superconducting properties [68][69][70][71][72], which has been understood by in-plane chemical pressure effects.…”

“…The single crystals of LnO 1−x F x BiS 2 can be easily exfoliated (layer by layer) because of the plate-like shape and the existence of a van der Waals gap between the BiS planes [46][47][48]. Notably, the van der Waals gap between two BiS planes became the essential feature when designing four-layer-type La 2 O 2 M 4 S 6 (M: metals) compounds [49][50][51][52], which is the central issue of this review article. The concept of designing new BiS2-based compounds with a thicker (four-layer-type) superconducting layer can be related to the case of the high-Tc cuprates [1,[53][54][55][56][57].…”

“…This trend in cuprates may be expected for other layered superconductors. [52], (b) YBa2Cu3O7−δ (YBCO) [51], and (c) Bi2Sr2Ca2Cu3Ox (BSCCO-2223) [55]. The concept of designing new BiS 2 -based compounds with a thicker (four-layer-type) superconducting layer can be related to the case of the high-T c cuprates [1,[53][54][55][56][57].…”

“…The continuous development of BiS 2 -based compounds has encouraged us to study the four-layer-type compounds [49][50][51][52]. Initially, the first four-layers-type LaOBiPbS 3 (equivalently described as La 2 O 2 Bi 2 Pb 2 S 6 to cover one unit cell) compound has been reported as a semiconductor and thermoelectric material [49].…”

Effect of Indium doping on the superconductivity of layered oxychalcogenide La2O2Bi3Ag1-xInxS6

“…The highest Tc up to 11 K was observed in a high-pressure phase of LaO1-xFxBiS2 [12][13][14][15][16]. Recently, we reported superconductivity in the oxychalcogenide La2O2Bi3AgS6 with Tc of 0.5 K [17]. Furthermore, we reported that Tc can be increased up to 2.4 K by Tin (Sn) substitution at the silver (Ag) site of La2O2Bi3AgS6 [18].…”