Lower Critical Fields of Superconducting PrFeAsO$_{1-y}$ Single Crystals
R. Okazaki, M. Konczykowski, C. J. van der Beek, T. Kato, K. Hashimoto, M. Shimozawa, H. Shishido, M. Yamashita, M. Ishikado, H. Kito, A. Iyo, H. Eisaki, S. Sha… 展开作者
R. Okazaki, M. Konczykowski, C. J. van der Beek, T. Kato, K. Hashimoto, M. Shimozawa, H. Shishido, M. Yamashita, M. Ishikado, H. Kito, A. Iyo, H. Eisaki, S. Shamoto, T. Shibauchi, Y. Matsuda
备注：
7 pages, 7 figures, accepted for publication in Phys. Rev. B
We have studied the lower critical fields H_{c1} of superconducting iron oxipnictide PrFeAsO_{1-y} single crystals for H parallel and perpendicular to the ab-planes. Measurements of the local magnetic induction at positions straddling the sample edge by using a miniature Hall-sensor array clearly resolve the first flux penetration from the Meissner state. The temperature dependence of H_{c1} for H || c is well scaled by the in-plane penetration depth without showing any unusual behavior, in contrast to previous reports. The anisotropy of penetration lengths at low temperatures is estimated to be ~ 2.5, which is much smaller than the anisotropy of the coherence lengths. This is indicative of multiband superconductivity in this system, in which the active band for superconductivity is more anisotropic. We also point out that the local induction measured at a position near the center of the crystal, which has been used in a number of reports for the determination of H_{c1}, might seriously overestimate the obtained H_{c1}-value.
Resistivity saturation in PrFeAsO$_{1-x}$F$_y$ superconductor: An evidence of strong electron-phonon coupling
我们测量了PrFeAsO $_{1-x}$ F $_y$样品在很宽的温度范围内的电阻率，以阐明电子-声子相互作用对正常和超导态性质的作用。$ρ$在170 K以上的线性T依赖性，随后在更高温度下的饱和行为是强电子-声子耦合的明显特征。通过对$ρ$的T依赖性的分析，我们估计了几个正常态参数，这些参数对理解该系统的超导电性起源是有用的。我们的研究结果表明，铁基氧磷属化合物是声子介导的BCS超导体，像Chevrel相和A15化合物。
In order to study the possible superconductivity at the polar surfaces of 1111-type iron-based superconductors, which is doped with a large amount of holes in spite of the electron doping in bulk materials, we have performed angle-resolved photoemission spectroscopy (ARPES) studies on superconducting PrFeAsO$_{1-y}$~crystals. We have indeed observed the opening of a superconducting gap on surface-derived hole pockets as well as on a bulk-derived hole pocket. The superconducting gap is found to open on the surface-derived hole pockets below the bulk $T_c$, which suggests that the surface superc…
Vortex dynamics and second magnetization peak in PrFeAsO$_{0.60}$F$_{0.12}$ superconductor
本文用直流磁化和动态磁化弛豫率$(Q)$测量研究了PrFeAsO $_{0.60}$ F $_{0.12}$超导样品中的涡旋动力学。超导不可逆磁化$M_s$的场依赖性揭示了第二磁化峰或鱼尾效应。大的$Q$值表明中等的涡旋运动和相对较弱的钉扎能。基于广义反演方案的数据分析表明，涡旋动力学可以用集体钉扎模型来描述。的临界电流的温度依赖性是一致的钉扎由于在晶格缺陷（$δl$钉扎）附近的平均自由程的空间变化。$Q$的温度和磁场依赖性表明，随着温度和磁场的增加，从弹性到塑性涡旋蠕变的交叉。最后，我们根据现有数据绘制了涡旋相图。
The magnetization of PrFeAsO$_{0.60}$F$_{0.12} sueprconductor
测量了PrFeAsO $_{0.60}$ F $_{0.12}$多晶样品的磁化强度随温度和磁场$(H)$的变化。观察到的总磁化强度是超导不可逆磁化强度（$M_s$）和顺磁磁化强度（$M_p$）的总和。对正常状态下$χ(T)$的直流磁化率的分析表明，磁化强度的顺磁分量来自Pr $^{+3}$磁矩。由磁化测量导出的晶粒内临界电流密度$(J_L)$大。$J_L(H)$曲线显示第二峰，其随着温度降低而向高场区域移动。在低场区域，高至场$H^*$的平台，随后是$J_L(H)$的幂律$H^{-5/8}$行为是强钉扎的特征。由磁化强度和电阻率数据得到了该超导体的涡旋相图。
We report the first determination of the in-plane complex optical conductivity of 1111 high-Tc superconducting iron oxypnictide single crystals PrFeAsO0.6F0.35 and thin films SmFeAsO1-xFx by means of bulk-sensitive conventional and micro-focused infrared spectroscopy, ellipsometry, and time-domain THz transmission spectroscopy. A strong itinerant contribution is found to exhibit a dramatic difference in coherence between the crystal and the film. Using extensive temperature-dependent measurements of THz transmission we identify a previously undetected 2.5-meV collective mode in the optical con…
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Inelastic X-ray Scattering Study of superconducting SmFeAs(O$_{1-x}$F$_{y}$) Single Crystals: Evidence for Strong Momentum-Dependent Doping-Induced Renormalizations of Optical Phonons
本文报道了SmFeAsO和超导SmFeAsO $_{0.6}$ F $_{0.35}$单晶晶格动力学的非弹性X射线散射实验。特别注意的是沿[100]方向的三个光学模式接近23 meV，偏振的FeAs平面的色散。值得注意的是，这些模式中的两个强烈重整化氟掺杂。这些结果提供了显着的洞察的能量和动量的依赖性的晶格的耦合到电子系统，并强调自旋-声子耦合的重要性，在超导铁磷属元素化物。
Single crystals of the unconventional superconductor UTe$_2$ have been grown in various conditions which result in different superconducting transition temperature as well as normal state properties. Stoichiometry of the samples has been characterized by the single-crystal X-ray crystallography and electron microprobe analyses. Superconducting samples are nearly stoichiometric within an experimental error of about 1 \%, while non-superconducting sample significantly deviates from the ideal composition. The superconducting UTe$_2$ showed that the large density of states was partially gapped in …
We have combined elastic and inelastic neutron scattering techniques, magnetic susceptibility and resistivity measurements to study single-crystal samples of K$_x$Fe$_{2-y}$Se$_2$, which contain the superconducting phase that has a transition temperature of $\sim$31 K. In the inelastic neutron scattering measurements, we observe both the spin-wave excitations resulting from the block antiferromagnetic ordered phase and the resonance that is associated with the superconductivity in the superconducting phase, demonstrating the coexistence of these two orders. From the temperature dependence of t…
The fluorine-doped rare-earth iron oxypnictide series SmFeAsO$_{1-x}$F$_x$ (0 $\leq x \leq$ 0.10) was investigated with high resolution powder x-ray scattering. In agreement with previous studies, the parent compound SmFeAsO exhibits a tetragonal-to-orthorhombic structural distortion at T$\rm{_{S}}$~=~130~K which is rapidly suppressed by $x \simeq$ 0.10 deep within the superconducting dome. The change in unit cell symmetry is followed by a previously unreported magnetoelastic distortion at 120~K. The temperature dependence of the thermal expansion coefficient $α_{V}$ reveals a rich phase diagr…
Superconducting Sm(O,F)BiS2 single crystals were successfully grown using KI-KCl flux. The obtained single crystals were flat-shaped and their size was 500um. The structure and composition of the obtained single crystals were obtained using X-ray diffraction and X-ray spectroscopy. The lattice constants of the obtained Sm(O,F)BiS2 single crystals were evaluated to be a = 3.9672(4) A and c = 13.417(6) A, while their F/(O + F) molar ratio was approximately 0.17. The superconducting transition temperature of the obtained Sm(O,F)BiS2 single crystals was 4.8 K. This was different from the reported …
Cd-doped La(O,F)BiS2 single crystals were grown using a CsCl/KCl flux. The grown crystals have a plate-like shape with ~1-2 mm square size in a well-developed ab-plane. The Cd doping in the crystals was successfully characterized by single crystal X-ray diffraction and electron probe microanalysis techniques. The superconductivity of La(O,F)BiS2 was gradually suppressed with Cd doping. The superconducting transition temperature with zero resistivity of La(O0.54F0.46)(Bi0.92Cd0.08)S2 was 2.3 K. The Cd doping does not change the superconducting anisotropy so much, albeit the considerable suppres…
We use spatially-resolved transport techniques to investigate the superconducting properties of single crystals La$_{2-x}$Ba$_x$CuO$_4$. We find a new superconducting transition temperature $T_{cs}$ associated with the ab-plane surface region which is considerably higher than the bulk $T_c$. The effect is pronounced in the region of charge carrier doping $x$ with strong spin-charge stripe correlations, reaching $T_{cs}=36$ K or 1.64$T_c$.
NbBiCh$_3$ (Ch = S, Se) misfit-layered superconducting single crystals were successfully grown using a CsCl/KCl flux for the first time. The obtained crystals had a well-developed habit parallel to the c-plane with a typical width of 1-2 mm and thickness of 10-40 um. The superconducting transition temperatures with zero resistivity of NbBiS$_3$ single crystals obtained from the nominal composition of Nb0.9Bi1.2S3 was 0.31 K, and that value of the NbBiSe$_3$ single crystals grown from the stoichiometry composition (NbBiSe$_3$) was 2.3 K. Sharp decreases in electric resistivity and magnetic susc…
