High-throughput research on superconductivity

As an essential component of the Materials Genome Initiative aiming to shorten the period of materials research and development, combinatorial synthesis and rapid characterization technologies have been playing a more and more important role in exploring new materials and comprehensively understanding materials properties. In this review, we discuss the advantages of high-throughput experimental techniques in researches on superconductors. The evolution of combinatorial thin-film technology and several high-speed screening devices are briefly introduced. We emphasize the necessity to develop new high-throughput research modes such as a combination of high-throughput techniques and conventional methods.

Different behavior of upper critical field in Fe1-xSe single crystals

The temperature dependences of upper critical field(Hc2) for a series of iron-deficient Fe1-xSe single crystals are obtained from the measurements of in-plane resistivity in magnetic fields up to 9 T and perpendicular to the ab plane. For the samples with lower superconducting transition temperature Tc(< 7.2 K), the temperature dependence of Hc2 is appropriately described by an effective two-band model. For the samples with higher Tc( 7.2 K), the temperature dependence can also be fitted by a single-band Werthamer–Helfand–Hohenberg formula, besides the two-band model. Such a Tc-dependent change in Hc2(T) behavior is discussed in connection with recent related experimental results, showing an inherent link between the changes of intrinsic superconducting and normal state properties in the Fe Se system.

Doping effects of transition metals on the superconductivity of (Li,Fe)OHFeSe films

The doping effects of transition metals(TMs = Mn, Co, Ni, and Cu) on the superconducting critical parameters are investigated in the films of iron selenide(Li,Fe)OHFe Se. The samples are grown via a matrix-assisted hydrothermal epitaxy method. Among the TMs, the elements of Mn and Co adjacent to Fe are observed to be incorporated into the crystal lattice more easily. It is suggested that the doped TMs mainly occupy the iron sites of the intercalated(Li,Fe)OH layers rather than those of the superconducting Fe Se layers. We find that the critical current density J_(c) can be enhanced much more strongly by the Mn dopant than the other TMs, while the critical temperature T_(c) is weakly affected by the TM doping.

通过氮含量调控ZrN薄膜中的超导圆顶

超导圆顶作为非常规超导材料的一个常见特征,其存在经常被用来作为区分常规与非常规超导材料的判别标准.本文利用脉冲激光沉积氮化锆薄膜,并通过改变薄膜中的氮含量,实现了超导圆顶于绝缘态附近的调控。利用电学输运、磁性表征、太赫兹光谱、拉曼散射和透射电镜综合实验手段与密度泛函计算,作者发现氮化锆薄膜正常态存在从强绝缘到金属态再到弱绝缘的转变,其电阻率表现出类似于非常规超导的线性温度依赖到二次温度依赖特征.而氮化锆超导能隙及其转变温度符合BCS预期,其超导圆顶的演化与材料中电声耦合强度及结构无序相关,这项工作为“常规”超导材料中存在的“非常规”超导圆顶提供了强有力的证据与实例.

Preparation of spatially uniform monolayer FeSexTe1−x(0

Spatially uniform high-temperature superconducting films are highly desirable for exploring novel properties and popularizing applications.To improve the uniformity,we fabricate monolayer FeSexTe1−x(0<x≤1)films on SrTiO3(001)by topotactic reaction of monolayer FeTe films with selenium.Using in situ low-temperature scanning tunneling microscopy/spectroscopy,we demonstrate atomic-level uniformity of element distribution and well-defined superconducting gaps of~15 meV in FeSexTe1−x films.In particular,the monolayer FeSe films exhibit fewer line defects and higher superfluid density as evidenced by sharper coherence peaks than those prepared by the co-evaporation method.Our results provide a promising way to optimize sample quality and lay a foundation for studying new physics and drawing reliable conclusions.

Surface morphology and electronic structure in stoichiometric superconductor CaKFe_(4)As_(4) robed by scanning tunneling microscopy/spectroscopy

CaKFe_(4)As_(4) is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morphology and electronic structure of CaKFe_(4)As_(4) single crystal were systematically investigated. The cleaved CaKFe_(4)As_(4) showed various morphologies, such as atomically resolved 1×1, 1×2, and √2×√2 lattices. By analyzing the geometrical correlations of these morphologies, the 1×1 and 1×2 lattices were identified as the original and reconstructed As layers, respectively, whereas the √2×√2 lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer. The superconducting energy gap of 7.3 me V and bosonic mode of 12.7 me V were resolved in the scanning tunneling spectra. In addition, the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques, indicating that the electronic structures of CaKFe_(4)As_(4) were insensitive to the surface reconstructions. Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.