Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which has the highest TC (about 4.6 K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi2Bi2O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electronic factors, which can be responsible for the increased transition temperature for BaTi2Bi2O (as compared with related pnictide-oxides BaTi2As2O and BaTi2Sb2O), are discussed.
Analogy between two-dimensional dislocation systems and layered superconductors
利用我们的模型与层状超导体之间的相似性，我们提出了一种对二维位错系统施加外应力的一致处理方法。在后一个模型中使用数学上严格的实空间重正化群（RG）计算的结果，我们扩展了Khantha { \it et al.}从我们的递归关系的非线性方程导出的转变温度作为施加的应力的函数。我们的结果进行了比较Khantha的模型的预测为三个特定的材料和偏差的原因进行了讨论。我们的模型可能的扩展进行了概述。
Polycrystalline sample of the new layered superconductor Bi4O4S3 is successfully synthesized by solid-state reaction method by using Bi, S and Bi2O3 powders with one step reaction. The superconducting transition temperature (Tconset=4.5 K), the zero resistance transition temperature (Tc0=4.07 K) and the diamagnetic transition temperature (4.02 K at H=10 Oe) were confirmed by electrical transport and magnetic measurements. Also, our results indicate a typical type II-superconductor behavior. In addition, a large thermoelectric effect was observed with a dimensionless thermoelectric figure of me…
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…
Based on the London equation, we use a rotor-free vector potential ${\bf A}$, and current measurements by a SQUID, to determine the superconducting Pearl length $Λ$, and coherence length $ξ$, of ultra-thin, ring shaped, MoSi films, as a function of thickness $d$ and temperature $T$. We find that $ξ$ is a function of $d$ with a jump at $ξ\sim d \sim 5$nm. At base temperature the superconducting stiffness, defined by $1/λ^2=1/(Λd)$, is an increasing function of $T_c$. Similar behavior, known as the Uemura plot, exist in bulk layered superconductors, but with doping as an implicit parameter. We a…
Complex conductivity in strongly fluctuating layered superconductors
本文用含时的Ginzburg-Landau方法计算了磁场作用下层状第二类超导体的复涨落电导率。超导体的层状结构由Lawrence-Doniach模型解释，而动力学中的非线性相互作用项在自洽高斯近似下处理。在高$T_{c}$材料中，$H-T$图的大部分属于涡旋液相。给出了所有朗道能级贡献之和的显式表达式，该表达式基本上适用于整个相，并与高$T_{c}$超导体$_{2}$ $_{3}$ O $_{7-δ}$的实验数据进行了比较.以上的交叉到“正常相”，我们的结果与以前得到的一致。
In BiS$_2$-based layered superconductors,the existence of gap nodes on Fermi-surface curves has been suggested from angle-resolved photoemission spectroscopy measurements, whereas the conventional $s$-wave gap has been proposed from measurements of superfluid density and thermal conductivity. To reconcile these two distinct experimental results of the gap node, we investigate nonmagnetic impurity effects in the superconductor with a disconnected pocketlike Fermi-surface structure. Then, we claim that the seemingly contradictory situation concerning the gap node is resolved by a concept of dirt…
We report impact of hydrostatic pressure on the newly discovered BiS2 based superconductors. In last couple of years the new BiS2 based superconductor attracted great attention of the condensed matter physics community. These new layered BiS2-based compounds are very sensitive to the concentration of carriers doping and pressure that cause profound changes in their physical properties with appearance of superconductivity in the vicinity of their insulating/semiconducting state. The BiS2-based new compounds are expected to provide us with the next stage of exploring new superconductors and to d…
Superconductivity arises from two distinct quantum phenomena: electron pairing and long-range phase coherence. In conventional superconductors, the two quantum phenomena generally take place simultaneously, while the electron pairing occurs at higher temperature than the long-range phase coherence in the underdoped high-Tc cuprate superconductors. Recently, whether electron pairing is also prior to long-range phase coherence in single-layer FeSe film on SrTiO3 substrate is under debate. Here, by measuring Knight shift and nuclear spin-lattice relaxation rate, we unambiguously reveal a pseudoga…
Electronic band structure and Fermi surface for new layered superconductor LaO0.5F0.5BiS2 in comparison with parent phase LaOBiS2 from first principles
Here presented a systematic study of superconductor-constriction-superconductor contacts realized by a break-junction technique in layered superconductors. Depending on the constriction transparency the tunneling and SnS-Andreev spectroscopies could be used, for the direct determination of values of superconducting gaps, characteristic BCS-ratios and gap temperature dependences in cuprate superconductors, magnesium diboride, novel pnictides and chalcogenides. Basing on these data, one can estimate the gap anisotropy magnitude as well as values of electron-boson coupling constants. We discuss t…
Theoretical investigation of the four-layered self-doped high-T$_c$ superconductors: evidence of pair tunneling effect
基于四层自掺杂$t-J$模型和从玻色子平均场方法，我们从理论上研究了电子掺杂层和空穴掺杂层的超导电性。相邻层通过单电子层间跳跃和对隧穿效应耦合。电子掺杂带的超导能隙大小几乎是空穴掺杂带的两倍，这与我们以前对高T $_c$超导体中电子-空穴不对称性的理解相反，但与最近在四层材料Ba $_2$ Ca $_3$ Cu $_4$ O $_8$ F $_2$中的角度分辨光电子能谱实验一致。我们的结果表明，对隧穿效应是重要的检查多层超导材料。
