Superconductivity in Bi_2−x Sb _x Te_3−y Se _y (x = 1.0 and y = 2.0) under pressure

Abstract

The crystal structure of BiSbTeSe 2 (Bi 2−x Sb x Te 3−y Se y (x = 1.0 and y = 2.0)) at 0-29 GPa is investigated through synchrotron x-ray diffraction (XRD) and two structural phase transitions are discovered. The stoichiometry of BiSbTeSe 2 employed in this study is Bi 1.19(4) Sb 0.81(4) Te 0.83(4) Se 2.17(4) , as determined from energy-dispersive x-ray spectroscopy. The sample demonstrated structural transitions, from a rhombohedral structure (space group no 166, R 3m) (phase I) to a monoclinic structure (space group no 12, C2/m) (phase II), and from phase II to a 9/10-fold monoclinic structure (space group no 12, C2/m) (phase III). The temperature dependence of resistance (R-T plot) exhibited a semiconducting behavior in a low pressure range and changed from semiconducting to metallic behavior with increasing pressure. Pressure-driven superconductivity is observed above 9.1 GPa in Bi 1.19(4) Sb 0.81(4) Te 0.83(4) Se 2.17(4) . The pressure phase corresponds to phase II. The superconducting transition temperature, T c , increased with pressure. The maximum T c value is 8.3 K at 19.1 GPa. The magnetic field dependence of T c in phase II of Bi 1.19(4) Sb 0.81(4) Te 0.83(4) Se 2.17(4) is proceeded by a p-wave polar model, indicating topologically nontrivial superconductivity. In addition, the emergence of superconductivity and the change in superconducting behavior are closely associated with the structural transitions.

Superconducting Properties of Pd1–xPtxBi2 over a Wide Pressure Range

“…The plots of H c2 versus T (Figure b) were constructed based on T c against each H , providing a value of H c2 L (0) (=0.889 T) based on formula . The h *– t plot (Figure c) indicates that the plot did not follow a simple s-wave dirty/clean limit mode, , but a p-wave polar model , similar to Bi 2 Se 3 , Sr- and Ag-doped Bi 2 Se 3 , , and Bi 2– x Sb x Te 3– y Se y , under pressure. This result was more unambiguous than that of the h *– t plot of β-PdBi 2 at 10.7 GPa.…”

“…Moreover, Fermi level tuning can be conducted by altering the values of x and y in Bi 2– x Sb x Te 3– y Se y . , Element doping of Bi 2 Se 3 often results in superconductors, such as Cu-doped Bi 2 Se 3 ( T c = 3.8 K) and Sr-doped Bi 2 Se 3 ( T c = 2.57 K) . The application of pressure to various topological insulators, such as Bi 2 Se 3 , metal-doped Bi 2 Se 3 , , and Bi 2– x Sb x Te 3– y Se y , , leads to superconductivity. The application of pressure to Sr 0.065 Bi 2 Se 3 yields three different superconducting phases .…”

Pressure-induced structural transitions, alloying and superconductivity in topological insulators Bi2Te2Se and Bi2Se2Te

“…Highly consistent phase transitions were also observed in Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 , 15 but the authors assigned the last high-pressure phase to the BCT structure. Besides, the wide low angle diffraction peak was also observed in Bi 2− x Sb x Te 2 Se ( x = 0, 0.25, 0.5, and 1.0) 16 and BiSbTeSe 2 17 upon compression. He et al considered that both Bi 2 Te 2 Se and BiSbTeSe 2 follow the phase transition sequence α-Bi 2 Te 3 phase → β-Bi 2 Te 3 phase → 9/10-fold C 2/ m , 16,17 while a γ-Bi 2 Te 3 structure was additionally observed in Bi 2− x Sb x Te 2 Se ( x = 0.25, 0.5, and 1.0).…”

“…Due to the low melting point of components in A 2 B 3 (A = Bi and Sb; B = Se, Te, and S), the compounds prepared by the traditional Stockbarger-Bridgman method tend to deviate from the expected stoichiometry. [14][15][16][17][18][19] In order to obtain stoichiometric Bi 2 Te 2 Se and Bi 2 Se 2 Te, the raw powders Bi, Te, and Se with a purity of 99.999% from Alfa Aesar were mixed according to the stoichiometric ratio of 2 : 2 : 1 and 2 : 1 : 2 (Bi : Te : Se), respectively. The mixtures were shaped into a cylinder with 5 mm diameter and 4 mm thickness using cold press (at least three pieces of each compound), inserted into an h-BN crucible with 12.4 mm outer diameter (5 mm inner diameter) and 11 mm length, and loaded into six-anvil high pressure apparatus for a high-pressure synthesis (HPS) experiment ( pressure: 1 GPa, temperature: 800 °C, duration: 60 min).…”

“…Besides, the wide low angle diffraction peak was also observed in Bi 2−x Sb x Te 2 Se (x = 0, 0.25, 0.5, and 1.0) 16 and BiSbTeSe 2 17 upon compression. He et al considered that both Bi 2 Te 2 Se and BiSbTeSe 2 follow the phase transition sequence α-Bi 2 Te 3 phase → β-Bi 2 Te 3 phase → 9/10-fold C2/m, 16,17 while a γ-Bi 2 Te 3 structure was additionally observed in Bi 2−x Sb x Te 2 Se (x = 0.25, 0.5, and 1.0). 16 In contrast, on the basis of highpressure XRD and first-principles calculations, Zhao et al reported that Bi 2 Te 2 Se, BiSbTeSe 2 and Sb 2 Te 2 Se transform from the rhombohedral structure into a β-Bi 2 Te 3 phase, 18 then to a BCT structure as pressure was increased, without the γ-Bi 2 Te 3 phase.…”