A reasonable cause of absence of hump structure in thermal conductivity of MgB2 below the superconducting transition temperature (Tc) lies in the appearance of multigap structure. The gaps of lower magnitude can be suppressed by defects so that this system becomes effectively a single gap superconductor. When such a situation is created, it is hoped that thermal conductivity will show hump below Tc. Proceeding along these lines, a sample of MgB2 with a relatively higher residual resistivity (33.3 mili-Ohm-cm)has been found to show a hump structure below Tc. The actual electronic thermal conductivity kel of this sample is less than that expected from the Wiedeman- Franz law by more than a factor of 2.6 in the considered temperature range. Modifying the Wiedeman- Franz law for the electronic contribution by replacing the Lorenz number by an effective Lorenz number Leff (L0) we have obtained two sets of kel, namely those with Leff = 0.1L0 and 0.2L0. Corresponding to these two sets of kel, two sets of the phonon thermal conductivity kph are obtained. kph has been analyzed in terms of an extended Bardeen- Rickayzen- Tewordt theory. The main result of this analysis is that the hump structure corresponds to a gap ratio of 3.5, and that large electron-point defect scattering is the main source of drastic reduction of the electronic thermal conductivity from that given by the usual Wiedeman- Franz law.
On the Origin of Peak-dip-hump Structure in the In-plane Optical Conductivity of the High $T_C$ Cuprates; Role of Antiferromagnetic Spin Fluctuations of Short Range Order
The entanglement of charge density wave (CDW), superconductivity, and topologically nontrivial electronic structure has recently been discovered in the kagome metal $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) family. With high-resolution angle-resolved photoemission spectroscopy, we study the electronic properties of CDW and superconductivity in CsV$_3$Sb$_5$. The spectra around $\bar{K}$ is found to exhibit a peak-dip-hump structure associated with two separate branches of dispersion, demonstrating the isotropic CDW gap opening below $E_{\rm F}$. The peak-dip-hump lineshape is contributed by linearly di…
Modeling Study of the Dip/Hump Feature in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ Tunneling Spectroscopy
在Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$（Bi-2212）上的高温超导体的隧穿谱可重复地显示出在高于间隙电压的电压下以dip-hump形式的高偏压结构。核心问题是，这一特征是否源于正常态背景，或者是超导机制所固有的。我们通过生成一组模型电导曲线来解决这个问题-一个“正常状态”电导，考虑到诸如能带结构和可能的赝能隙的影响，以及一个纯超导状态电导。当结合时，结果表明，在实验电导曲线中存在的dip-hump特征不能天真地归因于正常状态效应。特别是，在超导体-绝缘体-超导体数据中发现的最佳掺杂的Bi-2212，包括负的dI/dV的强倾角功能，不能是一个外在的赝能隙的后果。然而，这样的特征可以容易地由超导态密度中的状态守恒偏差引起，例如，强耦合效应。
The recent discovery of a direct link between the sharp peak in the electron quasiparticle scattering rate of cuprate superconductors and the well-known peak-dip-hump structure in the electron quasiparticle excitation spectrum is calling for an explanation. Within the framework of the kinetic-energy driven superconducting mechanism, the complicated line-shape in the electron quasiparticle excitation spectrum of cuprate superconductors is investigated. It is shown that the interaction between electrons by the exchange of spin excitations generates a notable peak structure in the electron quasip…
We performed thermal conductivity measurements on a single crystal of the ferromagnetic superconductorUCoGe under magnetic field. Two different temperature dependencies of the thermal conductivity are observed, for H//b linear at low magnetic field and quadratic for magnetic field larger than 1 Tesla. At the same field value, a plateau appears in the field dependency of the residual term of thermal conductivity. Such observations suggest a multigap superconductivity with a line of nodes in the superconducting gap.
Because of the important role of electron-boson interactions in conventional superconductivity, it has long been asked whether any similar mechanism is at play in high-temperature cuprate superconductors. Evidence for strong electron-boson coupling is observed in cuprates with angle-resolved photoemission spectroscopy (ARPES), in the form of a dispersion kink and peak-dip-hump structure. What is missing is evidence of a causal relation to superconductivity. Here we revisit the problem using the technique of time-resolved ARPES on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. We focus on the peak-dip-hump str…
Microwave conductivity experiments can directly measure the quasiparticle scattering rate in the superconducting state. We show that this, combined with knowledge of the Fermi surface geometry, allows one to distinguish between closely related superconducting order parameters, e.g., d$_{x^2-y^2}$ and d$_{xy}$ superconductivity. We benchmark this method on YBa$_2$Cu$_3$O$_{7-δ}$ and, unsurprisingly, confirm that this is a d$_{x^2-y^2}$ superconductor. We then apply our method to $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, which we discover is a d$_{xy}$ superconductor.
Absence of nodes in the energy gap of the high-temperature electron-doped Pr1.85Ce0.15CuO4-y superconductor using thermal conductivity and specific heat measurements
To shed light on the mechanism responsible for the in-plane resistivity anisotropy in the nematic phase of the iron-based superconductors, we investigate the impact of spin fluctuations on the anisotropic AC conductivity. On the one hand, the scattering of electrons off magnetic fluctuations causes an anisotropic scattering rate. On the other hand, the accompanying Fermi velocity renormalization contributes to both the plasma frequency and the scattering rate in antagonistic ways, giving rise to anisotropies in these quantities that exactly cancel each other in the DC limit. As a result, the e…
FeSe is an iron-based superconductor of immense current interest due to the large enhancements of Tc that occur when it is pressurized or grown as a single layer on an insulating substrate. Here we report precision measurements of its superconducting electrodynamics, at frequencies of 202 and 658 MHz and at temperatures down to 0.1 K. The quasiparticle conductivity reveals a rapid collapse in scattering on entering the superconducting state that is strongly reminiscent of unconventional superconductors such as cuprates, organics and the heavy fermion material CeCoIn5. At the lowest temperature…
Charge density waves as the origin of dip-hump structures in differential tunneling conductance of cuprates: the case of $d$-wave superconductivity
计算了具有电荷密度波（CDW）的$d$波超导体与正常金属之间的非对称隧道结的电导-电压特性（CVC）。结果表明，它们在小电压$V$下具有V状形式，并且由于在其中一个$V$ -分支中存在CDW峰而在较大的$V$下是不对称的。电介质（CDW）序参量的空间散射将CDW峰涂抹成一个驼峰，并诱导出在这种结中观察到的典型CVC的峰-谷-驼峰结构（PDHS）。当温度高于超导临界温度时，PDHS演变为赝能隙凹陷。结果与Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$和YBa $_{2}% $ Cu $_{3}$ O $_{7-δ}$的扫描隧道显微镜数据一致。
Zero temperature optical conductivity of ultra-clean Fermi liquids and superconductors
我们计算了零温下洁净金属和超导体的低频光学电导率σ（w），忽略了杂质和声子的影响。一般来说，sigma的频率和温度依赖性几乎没有共同之处。例如，对于三维的小费米面（但不是二维的），我们发现对于低w，Re σ（w>0）=常数，这对应于散射率γ与w^2成比例，即使在没有Umklapp散射的情况下，当T^2对γ没有贡献时。本文的主要部分详细讨论了二维d波超导体的光学电导率，其中Re sigma（w>0）\propto w ^4对应于最小频率，Umklapp过程通常在小于最大能隙Δ的两倍的有限阈值w_0之上平滑地设置。在节点位于（pi/2，pi/2）的情况下，使得它们之间的直接Umklapp散射是可能的，得到Re sigma（w）\propto w ^2。
The thermal conductivity of the iron-based superconductor FeSe was measured at temperatures down to 50 mK in magnetic fields up to 17 T. In zero magnetic field, the electronic residual linear term in the T = 0 limit, κ_0/T, is vanishingly small. Application of a magnetic field H causes no increase in κ_0/T initially. Those two observations show that there are no zero-energy quasiparticles that carry heat and therefore no nodes in the superconducting gap of FeSe. The full field dependence of κ_0/T has the classic shape of a two-band superconductor, such as MgB2: it rises exponentially at very l…
In-plane superfluid density and microwave conductivity of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: evidence for d-wave pairing and resilient quasiparticles
Anisotropic microwave conductivity of cuprate superconductors in the presence of CuO chain induced impurities
在动能驱动的超导机制下，研究了邻位Ⅱ型$_2$的微波电导各向异性.邻位-Ⅱ $_2$ $_3$ O $_{6.50}$的特征在于填充和空$\hat{b}$轴CuO链的周期性交替。考虑CuO链诱导的扩展各向异性杂质散射，基于准粒子激发和散射过程的节块近似，再现了邻位Ⅱ型$_2$微波电导各向异性的主要特征，包括$\hat{a}$轴和$\hat{b}$轴微波电导的能量和温度依赖性的强度和线形.我们的研究结果也证实了$\hat{b}$轴CuO链诱导杂质是各向异性的主要来源。
Analysis of the resonance peak and magnetic coherence seen in inelastic neutron scattering of cuprate superconductors: a consistent picture with tunneling and conductivity data
