Pressure dependence of the thermodynamic critical field $B_{\mathrm{c}}$ in elemental aluminum was studied by means of the muon-spin rotation/relaxation technique. Pressure enhances the deviation of $B_{\mathrm{c}}(T)$ from the parabolic behavior, expected for a typical type-I superconductor, thus suggesting the weakening of the gap ratio $\langleα\rangle=\langle Δ\rangle/k_{\mathrm{B} }T_{\mathrm{c}}$ ($\langleΔ\rangle$ is the average value of the superconducting energy gap, $T_{\mathrm{c}}$ is the transition temperature and $k_{\mathrm{B}}$ is the Boltzmann constant). With the pressure increase from 0.0 to $\simeq1.6$ GPa, $\langleα\rangle$ decreases almost linearly from 1.73 to 1.67. Our results imply, therefore, that in elemental aluminum the gap ratio $\langleα\rangle$ is smaller than the weak-coupled BCS prediction $α_{\mathrm{BCS}}\simeq1.764$ and it is even further reduced under pressure.
Anisotropic Scattering and Anomalous Transport in a High Temperature Superconductor
高温铜氧化物超导体的金属态与教科书上的金属态有很大的不同。这种非常规状态的起源，其特点是不寻常的和独特的温度依赖性的运输性能，仍然没有得到解决，尽管激烈的理论努力。我们的理解是受损的，我们无法确定实验的温度和动量的依赖性的运输散射率。在这里，我们使用一种新的磁输运探针表明，不寻常的温度依赖性的电阻率和霍尔系数在高掺杂TlPDMATHABMM Ba $_2$ CuO $_{6+δ}$起源于两个不同的非弹性散射通道。一个通道是由于传统的电子-电子散射，而另一个是高度各向异性的，具有与超导能隙相同的对称性和随温度近似线性增长的幅度。观察到的形状和各向异性对金属态理论提出了严格的限制。此外，在重掺杂的非超导铜氧化物中，似乎不存在这种各向异性散射项，这表明这种散射的起源与超导性本身之间存在密切联系。
Anomalous Zeeman response in coexisting phase of superconductivity and spin-density wave as a probe of extended $s$-wave pairing structure in ferro-pnictide
Anomalous Superconducting-Gap Structure of Slightly Overdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$
利用三维角分辨光电子能谱（3D angle-resolved photoemission spectroscopy，3D）研究了轻度过掺杂超导体Ba（Fe $_{1-x}$ Co $_{x}$）$_{2}$ As $_{2}$（$x=0.1$）的各向异性超导能隙（SC-gap）结构.在布里渊区中心观察到两个空穴费米面（FS），在区角观察到一个内电子FS，在三维动量空间中显示出几乎各向同性的SC带隙。然而，外部电子FS表现出各向异性SC间隙与节点或间隙最小值周围的M和A点。不同的各向异性获得的SC之间的差距外，内电子FS不能预期从所有的理论预测与自旋波动，轨道波动，和两者的竞争。我们的研究结果为铁磷属元素化物超导体的SC机制提供了新的见解。
We investigate transverse charge and spin dc supercurrents in a ferromagnet coupled to a superconductor where the ferromagnet has inhomogeneous magnetic structure. These transverse supercurrents arise from non-trivial structure of the magnetization. The magnetic structure manifested in the transverse charge supercurrent is essentially different from that discussed in the context of anomalous Hall effect, reflecting the disspationless nature of supercurrent. Possible candidates of magnetic structure to verify our prediction are also discussed.
In this work, we show that the CuAl2-type superconductor CoZr2 and alloyed systems exhibit anomalous thermal expansion in a wide temperature range. We performed neutron powder diffraction and X-ray powder diffraction on CoZr2 and observed remarkably anisotropic thermal expansion with a c-axis negative thermal expansion constant of αc < -15 μK-1 in a wide temperature range of T = 50-573 K. With decreasing temperature, the lattice constant a decreases, while the lattice constant c continuously increases in CoZr2. The origin of the anisotropic shrinkage/expansion of the a-axis/c-axis by cooling i…
