Tetragonality induced superconductivity in anti-ThCr₂Si₂-type RE₂O₂Bi (RE = rare earth) with Bi square nets

Abstract

We report a series of layered superconductors, anti-ThCr2Si2-type RE2O2Bi (RE = rare earth), composed of electrically conductive Bi square nets and magnetic insulating RE2O2 layers. The superconductivity was induced by separating Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in RE2O2 layers. Intriguingly, the transition temperature of all RE2O2Bi including nonmagnetic Y2O2Bi was approximately scaled by the unit cell tetragonality (c/a), implying a key role of relative separation of the Bi square nets to induce the superconductivity.

Increased hole mobility in anti-ThCr2Si2-type La2O2Bi co-sintered with alkaline earth metal oxides for oxygen intercalation and hole carrier doping

“…The a-axis length was almost constant irrespective of xCa, xSr, and xBa values, while the c-axis length was expanded with increasing xCa, xSr, and xBa. The c-axis length was almost the same for each xCa and xBa, and those for each xSr showed a larger increase in proportion to xSr.From SEM-EDX measurements, Ca was fully precipitated from La2O2Bi matrix (Fig.S2 †), indicating that CaO served as an oxygen intercalant without Ca substitution with La, as was reported in other RE2O2Bi 13,14. On the other hand, Sr was not significantly precipitated, but incorporated in La2O2Bi matrix (Fig.S3†), representing homogeneous Sr substitution with La.…”

“…S2 †), indicating that CaO served as an oxygen intercalant without Ca substitution with La, as was reported in other RE2O2Bi. 13,14 On the other hand, Sr was not significantly precipitated, but incorporated in La2O2Bi matrix (Fig. S3 †), representing homogeneous Sr substitution with La.…”

“…10,11 Intriguingly, the electronic properties are significantly influenced by their lattice constants: metal-insulator transition induced by expanding aaxis length via RE substitution 10 and superconducting transition of metallic RE2O2Bi (RE = Y, Tb, Dy, Er, and Lu) induced by expanding c-axis length via excess oxygen intercalation. [12][13][14] Recently, insulating La2O2Bi with the longest a-axis length was transformed into a metallic one with high hole mobility of 85 cm 2 V −1 s −1 by expanding the c-axis length via oxygen intercalation. 15 In this study, La2O2Bi was co-sintered with alkaline earth metal oxides (CaO, SrO, and BaO).…”

Antiferromagnetic structure and magnetic properties of Dy2O2Te: An isostructural analog of the rare-earth superconductors R2O2Bi

“…This kind of materials demonstrate numerous intriguing physical properties such as metal-insulator transition [27][28][29], charge density wave [30,31] and Kondo effect [32]. Most interestingly, R 2 O 2 Bi with heavy rare-earth elements (R = Tb, Dy, Er, Lu, Y) were recently discovered to be superconducting below ∼2 K via excess oxygen incorporation [33][34][35]. Remarkably, Tb 2 O 2 Bi and Er 2 O 2 Bi are found to become antiferromagnetic in a first-ordered transition when they become superconductor, exhibiting the coexistence of antiferromagnetism with superconductivity according to the measurements of resistivity and susceptibility [27,[34][35][36].…”

“…There have existed numerous discussions on the superconducting properties and mechanism of R 2 O 2 Bi. For example, the superconductivity is considered as arising from the metallic Bi square nets and the unit cell tetragonality (c/a) is suggest to be closely related to superconducting transition temperature T c [35]. The superconducting Bi square nets are also associated with the possibilities of exploring topological superconductivity [34,37].…”