Note: Novel diamond anvil cell for electrical measurements using boron-doped metallic diamond electrodes

Robustness of superconductivity to external pressure in high-entropy-alloy-type metal telluride AgInSnPbBiTe5

High-entropy-alloy (HEA) superconductors are a new class of disordered superconductors. However, commonality of superconducting characteristics of HEA materials is unclear. Here, we have investigated the crystal and electronic structure, and the robustness of superconducting states in a HEA-type metal telluride (MTe; M = Ag, In, Sn, Pb, Bi) under high pressure, and the results were compared with the pressure effects for a middle-entropy system (AgPbBiTe₃) and a reference system of PbTe. When the crystal structure is CsCl-type, all phases show superconductivity under high pressure but exhibit different pressure dependences of the transition temperature (T_c). For PbTe, its T_c decreases with pressure. In contrast, the T_c of HEA-type AgInSnPbBiTe₅ is almost independent of pressure, for pressures ranging from 13.0 to 35.1 GPa. Those results suggest that the robustness of superconductivity to external pressure is linked to the configurational entropy of mixing at the M site in MTe. Since the trend is quite similar to previous work on a HEA (Ti–Zr–Hf–Nb–Ta), where the robustness of superconductivity was observed up to ~ 200 GPa, we propose that the robustness of superconductivity under high pressure would be a universal feature in HEA-type superconductors.

Electrical Transport Measurements on Layered La(O,F)BiS2 under Extremely High Pressure

Layered La(O,F)BiS2 exhibits drastic enhancements of the superconducting transition temperature (Tc) under high pressure among the BiS2-based superconducting family. However, the high-pressure application beyond a high-Tc phase of the monoclinic structure has not been conducted. In this study, the electrical transport properties in La(O,F)BiS2 single crystal are measured under high pressures up to 83 GPa. An insulating phase without superconductivity is observed under a higher-pressure region above 16 GPa. Moreover, the sample exhibits metallicity and superconductivity above 60 GPa. The newly observed hidden semiconducting phase and reentrant superconductivity have attracted much attention in BiS2-based compounds.

High-Pressure Synthesis of Superconducting Sn3S4 Using a Diamond Anvil Cell with a Boron-Doped Diamond Heater

High-pressure techniques open exploration of functional materials in broad research fields. An established diamond anvil cell with a boron-doped diamond heater and transport measurement terminals has performed the high-pressure synthesis of a cubic Sn₃S₄ superconductor. X-ray diffraction and Raman spectroscopy reveal that the Sn₃S₄ phase is stable in the pressure range of P > 5 GPa in a decompression process. Transport measurement terminals in the diamond anvil cell detect a metallic nature and superconductivity in the synthesized Sn₃S₄ with a maximum onset transition temperature (T_c^onset) of 13.3 K at 5.6 GPa. The observed pressure-T_c relationship is consistent with that from the first-principles calculation. The observation of superconductivity in Sn₃S₄ opens further materials exploration under high-temperature and -pressure conditions.

Synthetic Route of Layered Titanium Nitride Chloride TiNCl Using Sodium Amide

A synthetic route in a closed system for layered titanium nitride chloride TiNCl has been developed using sodium amide NaNH₂ as a nitrogen source. A highly crystalline sample is obtained by an appropriate thermal decomposition of aminated titanium chloride. The obtained TiNCl was also characterized using electronic resistivity measurement and photoemission spectroscopy. TiNCl showed hopping conduction compatible with an in-gap state revealed by photoelectron spectroscopy. However, it appeared highly electron-doped, albeit without showing superconductivity. Comparison with the spectrum of superconducting sodium-doped samples suggests the presence of the microstructure required to exhibit superconductivity.

Setup for pressurizing thin films through the superconductor-insulator transition

We describe an experimental setup designed for transport measurement of thin disordered superconducting films as a function of pressure up to several GPa. We use a specially designed single screw diamond anvil cell that allows the gradual increase of high pressure at cryogenic temperatures. By depositing amorphous films of disordered superconducting indium oxide directly on the diamond, we avoid the effect of pressure-induced structural changes in the substrate. Using this technique, we are able to drive thin films through a pressure tuned superconductor-insulator transition.

Crystal Growth and High-Pressure Effects of Bi-Based Superconducting Whiskers

Three growth methods were tested for producing high-transition temperature superconducting Bi₂Sr₂Ca _n-1Cu _n O_2n+4+δ whiskers, employing different ways to focus a compressive stress and size effect of the precursors. First, thermographic imaging was used to investigate thermal stress from temperature distribution in the precursors during growth annealing. To enhance thermal stress in the precursors, a thermal cycling method and a Ag-paste coating method were proposed and found to significantly accelerate the whisker growth. The use of pulverized precursors also promoted whisker growth, possibly due to contribution from the vapor-liquid-solid growth mechanism. The obtained whiskers revealed the typical composition, diffraction patterns, and superconducting properties of the Bi-2212 phase. The proposed methods were able to stably produce longer whiskers compared to the conventional method. Using the obtained whiskers, electrical transport measurements under high pressure were successfully performed up to around 50 GPa.

High-pressure effects on superconducting properties and crystal structure of Bi-based layered superconductor La2O2Bi3Ag0.6Sn0.4S6

The effects of pressure on the superconducting properties of a Bi-based layered superconductor La₂O₂Bi₃Ag_0.6Sn_0.4S₆, which possesses a four-layer-type conducting layer, have been studied through the electrical resistance and magnetic susceptibility measurements. The crystal structure under pressure was examined using synchrotron x-ray diffraction at SPring-8. In the low-pressure regime, bulk superconductivity with a transition temperatureT_cof ∼4.5 K was induced by pressure, which was achieved by in-plane chemical pressure effect owing to the compression of the tetragonal structure. In the high-pressure regime above 6.4 GPa, a structural symmetry lowering was observed, and superconducting transitions with aT_c∼ 8 K were observed. Our results suggest the possible commonality on the factor essential forT_cin Bi-based superconductors with two-layer-type and four-layer-type conducting layers.

Pressure-induced superconductivity in SnSb2Te4

Here we firstly report the pressure-induced superconductivity in phase change materials SnSb₂Te₄. Single crystals of SnSb₂Te₄ were grown using a conventional melting-down method. The resistance under pressure was measured using an originally designed diamond anvil cell with boron-doped diamond electrodes. The temperature dependence of the resistance under different pressures has been measured up to 32.6 GPa. The superconducting transition of SnSb₂Te₄ appeared at 2.1 K ([Formula: see text]) under 8.1 GPa, which was further increased with applied pressure to a maximum onset transition temperature 7.4 K under 32.6 GPa.

Crystal Growth, Structural Analysis, and Pressure-Induced Superconductivity in a AgIn5Se8 Single Crystal Explored by a Data-Driven Approach

A high-throughput first-principles calculation-assisted data-driven approach based on an inorganic materials database named AtomWork was performed to explore new superconducting materials. Specific band structures of a small band gap and flat band at band edges were used in a screening procedure. Among the candidates studied, we focused on AgIn₅Se₈, which shows a high density of state at the Fermi level. Single crystals of AgIn₅Se₈ were successfully obtained via a melt and slow cooling method. The valence states in AgIn₅Se₈ were estimated to be Ag¹⁺, In³⁺, and Se^2- using X-ray photoelectron spectroscopy. An electrical transport property of resistance was measured under high pressure using an electrodes-inserted diamond anvil cell. The sample exhibited an insulator-to-metal transition with a drastic decrease of the resistance by increasing the pressure up to 24.8 GPa. A possibility of a pressure-driven phase transition below this pressure was indicated by an enthalpy calculation. At a higher pressure region of 52.5 GPa, a pressure-induced superconducting transition was observed at 3.4 K. The maximum transition temperature was increased up to 3.7 K under the pressure of 74.0 GPa.

Data-driven exploration of new pressure-induced superconductivity in PbBi2Te4

Candidate compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi₂Te₄ which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi₂Se₄ explored by the same data-driven approach. The PbBi₂Te₄ was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb²⁺, Bi³⁺ and Te^2- valence states in PbBi₂Te₄. The thermoelectric properties of the PbBi₂Te₄ sample were measured at ambient pressure and the electrical resistance was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistance decreased with increasing of the pressure, and pressure-induced superconducting transitions were discovered at 2.5 K under 10 GPa. The maximum superconducting transition temperature increased up to 8.4 K at 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials.