Three growth methods were tested for producing high-transition temperature superconducting Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$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 an 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 at up to around 50 GPa.
Using stress-controlled amorphous precursors, we have successfully grown large $Bi_{2}$$Sr_{2}$$Ca_{\textit{n}-1}$$Cu_{\textit{n}}$$O_{\textit{y}}$ (Bi-based) high-transition temperature superconducting whiskers. Especially, under a high compressive stress attained by 1 GPa pelletizing, the crystal size of a whisker was significantly enhanced up to 9.5 mm length (growth period: 96 h) which is 2.4 times larger than that of the conventional amorphous-precursors method. In addition, by using the stress-controlled precursors, the number of the obtained Bi-based whiskers were also increased by a fa…
Single-crystal whiskers of REBa2Cu3Ox (RE-123, RE: rare earth element) cuprate superconductors were successfully grown using Te-doped precursors utilizing the concept of high-entropy-alloys (HEAs) at the RE site. The obtained whiskers were 0.5-1.0 mm length with approximately 10 um thickness. The width of the flat surface, which corresponds to the ab-plane, was 10-50 um. The RE site of the grown whiskers could be easily substituted by large ionic radius RE elements (Gd, Dy, and Ho). Substitution with small ionic radius RE elements (Tm, Yb, and Lu) resulted in the opposite trend. The supercondu…
High-transition temperature superconducting whiskers of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ were successfully grown from pulverized amorphous precursors. The obtained whiskers revealed a typical composition and diffraction patterns of a superconducting Bi-2212 phase. The whiskers from tiny precursors exhibit a spiral feature, suggesting a contribution from the growth mechanism of both vapor-liquid-solid and compressive stress models. The proposed method provides longer whiskers against the growth period, compared with that from conventional root-growth method.
Evidence of a dominant Maki-Thompson process in the fluctuation conductivity of the Bi-2212 superconducting whiskers
本文报道了Bi_2Sr_2CaCu_2 O_（8 +x）微晶在零场下a轴涨落电导率的测量结果。良好的几何特征和原始的数据分析方法允许以高精度确定其温度行为。完全涨落理论的正确应用[A. A. Varlamov等人，Adv.Phys.48，655（1999）]，并对k_tilde因子作了较小的修正，得出结论：在整个感兴趣的温度范围内，异常MT项是最重要的贡献。更传统的替代解释的实验数据也进行了研究，并证明了它们的不一致性。这意味着一个s波对称的序参量，并提供了一个物理机制的预成型对的情况。
The effects of pressure on the superconducting properties of a Bi-based layered superconductor La2O2Bi3Ag0.6Sn0.4S6, 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 temperature Tc of ~ 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 h…
A recent experiment reported that robust superconductivity appears in NbTi alloys under ultrahigh pressures with an almost constant superconducting $T_c$ of ~19 K from 120 to 261.7 GPa [J. Guo et al., Adv. Mater. 31, 1807240 (2019)], which is very rare among the known superconductors. We investigate the origin of this novel superconducting behavior in NbTi alloys based on density functional theory and density functional perturbation theory calculations. Our results indicate that the pressure tends to transform NbTi alloys from a random phase to a uniformly ordered crystal phase, and the exotic…
Investigating the pressure dependence of the superconducting (SC) transition temperature $T_{\rm c}$ is crucial for understanding the SC mechanism. Herein, we report on the pressure dependence of $T_{\rm c}$ in the nonmagnetic topological line-nodal material CaSb$_2$, based on measurements of electric resistance and alternating current magnetic susceptibility. $T_{\rm c}$ initially increases with increasing pressure and peaks at $\sim$ 3.1~GPa. With a further increase in pressure, $T_{\rm c}$ decreases and finally becomes undetectable at 5.9~GPa. Because no signs of phase transition or Lifshit…
Density functional theory (DFT) based first-principles investigations of structural, elastic, electronic band structure, and optical properties of superconducting ternary phosphides (BaM2P2; M = Ni, Rh) have been carried out in this study. This is the first detailed pressure dependent study of these properties for the titled compounds. The calculated ambient condition properties are compared with existing experimental and theoretical results, where available. The pressure dependent variations of the electronic density of states at the Fermi level, N(EF), and the Debye temperature, thetaD, have…
Very recently carbon-rich NaC6 with sodalite-like structure has been predicted to show superconducting transition temperature above 100 K at relatively low applied (compared to high-Tc hydrides) hydrostatic pressures. We have investigated the pressure dependent structural, elastic, electronic, superconducting state, and optoelectronic properties of NaC6 in this study. Some important thermophysical properties have also been explored. The elastic properties along with Poisson's and Pugh's ratios and optoelectronic parameters are investigated for the first time. NaC6 was found to be structurally …
We have investigated the Pb-substitution effect on the superconductivity of NaCl-type In1-xPbxTe samples obtained using high-pressure synthesis. Polycrystalline samples with x = 0-0.8 were obtained, and the lattice parameter systematically increased by Pb substitution. The superconducting transition temperature (Tc ~3 K for x = 0) increased to 5.3 K (for x = 0.4) by Pb substitutions. According to the comparison of the electronic states between NaCl-type InTe and PbTe, we consider that the Pb substitution increases electron carriers. Possible mechanisms of the enhancement of Tc in this system h…
The measurement of superconductivity at above 200K in compressed samples of hydrogen sulfide and lanthanum hydride at 250K is reinvigorating the search for conventional high temperature superconductors. At the same time it exposes a fascinating interplay between theory, computation and experiment. Conventional superconductivity is well understood, and theoretical tools are available for accurate predictions of the superconducting critical temperature. These predictions depend on knowing the microscopic structure of the material under consideration, and can now be provided through computational…
Two Pressure-induced Superconducting Transitions in SnBi$_2$Se$_4$ Explored by Data-driven Materials Search: New Approach to Develop Novel Functional Materials Including Thermoelectric and Superconducting Materials
利用高通量的第一性原理计算从无机材料数据库中搜索了具有窄禁带和近带边平坦带的新型热电和超导材料的候选材料。在目标化合物中合成的SnBi $_2$ Se $_4$显示出354 meV的窄带隙，并且在环境压力下的热导率为1 W/Km。样品SnBi $_2$ Se $_4$在11.1 GPa下表现出金属-绝缘体转变，正如理论估计所预测的。在20.2GPa和47.3GPa下发现了两个压力诱导的超导转变。数据驱动的搜索是发现新功能材料的一种很有前途的方法。
Effect of pressure on magneto-transport properties in the superconducting and normal phases of the metallic double chain compound Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$
为了研究超导CuO双链的电子相图，我们报道了在低温（1.8-40 K）和不同磁场（14 T）下，外压对超导和非超导多晶样品Pr $_{2}$ Ba $_{4}$ Cu $_{7}$ O $_{15-δ}$的磁输运性质的影响.在烧结态非超导样品中，低温下磁电阻（MR）服从$H^{3/2}$的幂律，这与PrBa $_{2}$ Cu $_{4}$ O $_{8}$系统中MR的$H^{2}$依赖性不一致.超导相的负压力依赖性与Tomonaga-Luttinger液体理论的理论预测定性一致。常压下48 h还原的超导样品对$T > T_{c,on}=26.5$ K的MR没有明显的增加。与此相反，与超导样品的压力的应用程序，MR效应再现，也很好地拟合$H^{3/2}$。微翘曲费米面模型不仅解释了非超导样品的磁流变效应，而且与超导样品的压致磁流变现象的原因有关。
The superconducting systems emerging from topological insulators upon metal ion intercalation or application of high pressure are ideal for investigation of possible topological superconductivity. In this context, Sr-intercalated Bi$_2$Se$_3$ is specially interesting because it displays pressure induced re-entrant superconductivity where the high pressure phase shows almost two times higher $T_c$ than the ambient superconducting phase ( $T_C\sim$ 2.9 K). Interestingly, unlike the ambient phase, the pressure-induced superconducting phase shows strong indication of unconventional superconductivi…
Polycrystalline samples of Sr1-xRExFBiS2 (RE: La, Ce, Pr, Nd, and Sm) were synthesized via the solid-state reaction and characterized using synchrotron X-ray diffraction. Although all the Sr0.5RE0.5FBiS2 samples exhibited superconductivity at transition temperatures (Tc) within the range of 2.1-2.7 K under ambient pressure, the estimated superconducting volume fraction was small. This indicated the non-bulk nature of superconductivity in these samples under ambient pressure. A dramatic evolution of the bulk superconducting phases was achieved on applying an external hydrostatic pressure. Near …
In Phys. Rev. Lett. 102, 197002 (2009) it was reported that the element Eu becomes superconducting in the pressure and temperature range [84-142GPa], [1.8-2.75K]. The claim was largely based on ac susceptibility measurements. Recently reported ac susceptibility measurements on a hydride compound under pressure that appears to become superconducting near room temperature (Nature 586, 373 (2020)) cast serious doubt on the validity of the results for Eu as well as for the hydride. Here I present results that shed new light on the true behaviour of Eu. It is argued that the experiments on Eu have …
Pressure induced re-emergence of superconductivity in superconducting topological insulator Sr0.065Bi2Se3
最近发现的Sr $_x$ Bi $_2$ Se $_3$超导体为研究可能的拓扑超导电性提供了另一种理想的材料基础。在这里，我们报告说，在Sr $_{0.065}$ Bi $_{2}$ Se $_3$，周围的超导相是逐渐压低后，施加外部压力。在高压下，在6GPa以上出现第二相，最大$\sim$值为$\sim$ 8.3K。高压同步辐射X射线衍射和电输运性质的联合研究表明，Sr $_{0.065}$ Bi $_{2}$ Se $_3$的超导电性的重新出现与其在6 GPa附近从环境菱面体相到高压单斜相的结构相变，以及在25 GPa以上进一步到另一高压四斜相的结构相变密切相关.
