最近发现的铁磷族化合物超导体的正常态性质可能是理解其奇异超导性的关键。使用点接触光谱，我们表明，Andreev反射之间的外延薄膜的Ba（Fe $_{0.92}$ Co $_{0.08}$）$_2$作为$_2$和银尖可以看到在正常状态下的膜的温度$T\sim1.3T_c$，其中$T_c$是临界温度的超导体。只有当复超导序参量相位的强涨落所产生的超导对处于正常状态时，才能理解远高于$T_c$的Andreev反射。我们的结果提供了铁磷族化合物超导体正常态下存在相位非相干超导对的光谱证据。
英文摘要：
The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe$_{0.92}$Co$_{0.08}$)$_2$As$_2$ and a silver tip can be seen in the normal state of the film up to temperature $T\sim1.3T_c$, where $T_c$ is the critical temperature of the superconductor. Andreev reflection far above $T_c$ can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors.
We construct a family of translationally invariant lattice models with a large number ($N$) of orbitals at every site coupled together via single electron tunneling. By tuning the relative strength of the electronic bandwidth and on-site interactions, that have a modified Sachdev-Ye-Kitaev (SYK) form, we demonstrate a number of unusual features at strong coupling and in the large$-N$ limit. We find examples of (i) an intrinsic non-BCS superconducting instability arising out of an incoherent non-Fermi liquid metal, and, (ii) an instability of an incipient heavy Fermi liquid metal to superconduc…
In this study, we conducted various magnetotransport measurements on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ single crystals from which excess iron was sufficiently removed. Our results revealed that crossover from the incoherent to the coherent electronic state and opening of the pseudogap occur at high temperatures ($\approx$ 150 K for $x$ = 0.2). This is accompanied by a more substantial pseudogap and the emergence of a phase with a multi-band nature at lower temperatures (below $\approx$ 50 K for $x$ = 0.2) before superconductivity sets in. A comparison of these results with those of the as-grown (no…
The diamagnetism above the superconducting transition in underdoped La(1.9)Sr(0.1)CuO(4) revisited: Chemical disorder or phase incoherent superconductivity?
超导波动和不均匀性之间的相互作用提出了一个新的兴趣，由于最近的工作支持一个异常的[超越传统的高斯-金兹伯格-朗道（GGL）的情况下]抗磁性高于Tc在欠掺杂的铜酸盐。这一结论主要是基于低场等温磁化曲线中新异常的观察，与我们早期在欠掺杂La（1.9）Sr（0.1）CuO（4）[Phys. Rev. Lett. 84，3157（2000）]。这些看似内在的反常现象在各种有影响力的著作中被作为赝能隙区相位非相干超导性的“热力学证据”提出，这是目前铜酸盐超导体物理学的一个中心和有争议的问题。在这里，我们已经扩展了我们的磁化强度测量在La（1.9）Sr（0.1）CuO（4）的两个样品具有不同的化学无序，在其中一个接近与随机分布的Sr离子。对于该样品，相应的Tc分布可以近似为围绕平均Tc对称，而在最无序的样品中是强烈不对称的。在这两个样品中测量的磁化强度之间的比较提供了一个关键的检查所观察到的抗磁性异常，这是类似于那些声称由于相位波动由其他作者的化学无序起源。这一结论也适用于只受本征类化学无序影响的样品，提供了进一步的检查，即在正常状态下的赝能隙的打开不影响低掺杂铜酸盐的超导转变以上的本征抗磁性。它还表明，一旦这些障碍的影响被克服，剩余的前体抗磁性可以占在一个定量水平的GGL方法下的总能量截止。
We investigate theoretically the excitation of Higgs oscillations of the order parameter in superconductors by incoherent short pulses of light with frequency much larger than the superconducting gap. The excitation amplitude of the Higgs mode is controlled by a single parameter which is determined by the total number of quasiparticles excited by the pulse. This fact can be traced back to the universality of the shape of the light-induced quasiparticle cascade at energy below the Debye frequency and above the gap.
Modeling a normal/superconducting interface, we consider a semi-infinite wire whose edge is adjacent to a normal magnetic metal, assuming asymptotic convergence, away from the boundary, to the purely superconducting state. We obtain that the maximal current which can be carried by the interface diminishes in the small normal conductivity limit.
The pair breaking potential of individual magnetic impurities in s-wave superconductors generates localized states inside the superconducting gap commonly referred to as Yu- Shiba-Rusinov (YSR) states whose isolated nature makes them ideal building blocks for artificial structures that may host Majorana fermions. One of the challenges in this endeavor is to understand their intrinsic lifetime, $\hbar/Λ$, which is expected to be limited by the inelastic coupling with the continuum thus leading to decoherence. Here we use shot-noise scanning tunneling microscopy to reveal that electron tunnellin…
Evidence of incoherent carriers associated with resonant impurity levels and their influence on superconductivity in the anomalous superconductor Pb$_{1-x}$Tl$_x$Te
我们提出了一个相结合的实验和理论研究的费米表面的异常超导体Pb $_{1-x}$ Tl $_x$ Te作为铊浓度的函数的演化，绘制磁输运测量（Shubnikov de Haas振荡和霍尔系数），角度分辨光电子能谱（ARPES），和密度泛函理论（DFT）的电子结构的计算相结合。我们的结果表明，对于Tl浓度超过一个临界值的费米能量符合共振杂质态的Pb $_{1-x}$ Tl $_x$ Te，我们排除了存在一个额外的价带最大的费米能量。通过与非超导Pb $_{1-x}$ Na $_x$ Te的比较，我们认为这些状态在费米能级的存在提供了配对相互作用，从而也提供了这种材料的高温超导性。
Using multiple Andreev reflection (MAR) spectroscopy, we studied superconductor - normal metal - superconductor (SnS) semiballistic contacts with incoherent transport in overdoped pnictide superconductors BaFe$_{1.86}$Ni$_{0.14}$As$_2$ with critical temperature $T_c \approx 12$ K. We directly determined an anisotropic large gap with the characteristic ratios $2Δ_L^{\rm out}(0)/k_BT_c \approx 6$ and $2Δ_L^{\rm in}(0)/k_BT_c \approx 4$, almost isotropic small gap with $2Δ_S(0)/k_BT_c \approx 2$, and the temperature dependence of the resolved superconducting order parameters. Above the large gap …
In unconventional superconductors, it is generally believed that understanding the physical properties of the normal state is a pre-requisite for understanding the superconductivity mechanism. In conventional superconductors like niobium or lead, the normal state is a Fermi liquid with a well-defined Fermi surface and well-defined quasipartcles along the Fermi surface. Superconductivity is realized in this case by the Fermi surface instability in the superconducting state and the formation and condensation of the electron pairs (Cooper pairing). The high temperature cuprate superconductors, on…
