The weak localization effect on a linear absorption spectrum is investigated for disordered s-wave superconductors. The vertex correction is incorporated into the response function in a way that is consistent with the weak localization correction to a one-particle spectrum. The effect of interactions between electrons enhanced by their diffusive motion makes a major contribution to the correction term. Numerical calculations show that the weak localization effect suppresses the absorption by the excitation across the gap to a greater extent than that by thermal excitation, which is a similar tendency to the results of experiments. The ratio of the linear absorption with vertex corrections to that without the corrections shows a large variation at the frequency that is around twice the energy of the superconducting gap. This behavior represents a relationship between the weak localization effect on the linear absorption and that on the one-particle spectrum.
We discuss a new mechanism of microwave absorption in s- and d-wave superconductors, which arises in the presence of a dc supercurrent in the system. It produces a contribution to the ac conductivity that is proportional to the inelastic quasiparticle relaxation time. This contribution also determines the supercurrent dependence of the conductivity. It may significantly exceed the conventional contribution because in typical superconductors the inelastic relaxation time is several orders of magnitude longer than the elastic one. We show that the aforementioned contribution to the conductivity …
Enhanced microwave absorption, larger than that in the normal state, is observed in fine grains of type-II superconductors (MgB$_2$ and K$_3$C$_{60}$) for magnetic fields as small as a few $\%$ of the upper critical field. The effect is predicted by the theory of vortex motion in type-II superconductors, however its direct observation has been elusive due to skin-depth limitations; conventional microwave absorption studies employ larger samples where the microwave magnetic field exclusion significantly lowers the absorption. We show that the enhancement is observable in grains smaller than the…
We theoretically investigate the two-photon absorption spectrum of conventional s-wave superconductors. The calculation is carried out in the local limit at absolute zero. The direct excitation of quasiparticles is excluded under the condition that the frequency of the external field is lower than twice the magnitude of the superconducting gap. We calculate vertex corrections with the conserving approximation, and show that the amplitude mode is independent of the impurity scattering in the local limit. Because of this property, a diverging absorption edge appears in the dirty limit. We propos…
Residual absorption at zero temperature in d-wave superconductors
在具有弹性杂质散射的d波超导体中，并非所有可用的光谱权重都进入零温度下的凝聚态，这导致了剩余吸收。我们发现，对于一系列的杂质参数之间的中间耦合制度的玻恩（弱）和酉（强）的限制，显着的振子强度仍然表现出尖状行为的实部的光学电导率与向上的曲率作为频率的函数，以及准线性温度依赖性的超流密度。计算提供了一个解释的ortho-II YBa $_2$ Cu $_3$ O $_{6.5}$已被认为是异常的最近的数据。
Superconductivity in disordered systems close to an incipient localization transition has been an area of investigation for many years. It has been noted that in such highly disordered superconductors, anomalous spectral weight develops in their conductivity near and below the superconducting gap energy. In this work we investigate the low frequency conductivity in disordered superconducting NbN thin films close to the localization transition with time-domain terahertz spectroscopy. In the normal state, strong deviations from the Drude form due to incipient localization are found. In the super…
Electron energy loss near edge spectra (ELNES) has been calculated for two different Fe based superconducting material FeSe and FeTe using density functional theory (DFT). Fe K-edge absorption spectra consist of several features, origins of which are thoroughly described in light of partial density of states of constituent atoms. Here we have included "core-hole effect" and found drastic change in absorption spectra. Our results including core hole effect matches very well with experimental X-ray Absorption Near Edge Structure (XANES) results available in literature.
We study the localization and oscillation properties of the Majorana fermions that arise in a two-dimensional electron gas (2DEG) with spin-orbit coupling (SOC) and a Zeeman field coupled with a d-wave superconductor. Despite the angular dependence of the d-wave pairing, localization and oscillation properties are found to be similar to the ones seen in conventional s-wave superconductors. In addition, we study a microscopic lattice version of the previous system that can be characterized by a topological invariant. We derive its real space representation that involves nearest and next-to-near…
Two-dimensional weak localization effects in high temperature superconductor Nd{2-x}Ce{x}CuO{4-d}
A systematic study of the resistivity and Hall effect in single crystal Nd{2-x}Ce{x}CuO{4-d} films (0.12 < x < 0.20) is presented, with special emphasis on the low-temperature dependence of the normal state conductance. Two-dimensional weak localization effects are found both in a normally conducting underdoped sample (x = 0.12) and in situ superconducting optimally doped (x = 0.15) or overdoped (x = 0.18) samples in a high magnetic field B > B{c2}. The phase coherence time and the effective thickness of a CuO{2} conducting layer {d} (~ 1.5 A) have been estimated by fitting 2D weak localizatio…
Some Considerations on the Additional Absorption Peak in the c-axis Conductivity of Bilayer Cuprate Superconductors: Interpretation of the Changes Induced by a Parallel Magnetic Field and the Role of Bilayer Splitting
Kojima等人报道的在平行磁场作用下，低掺杂YBa 2 Cu 3 O 6. 6的c轴电导率的400 cm^{-1}峰的变化与超流峰的模型一致。我们的计算结果的c-轴响应的双层化合物具有明确的双层分裂带的介绍和讨论。对于中等值的双层分裂（Δ E相当于2 Delta_{max}）的超导态的光谱表现出额外的模式，这是由于冷凝和类似的早期的唯象方法之一。
Two dimensional topological superconductors (TS) host chiral Majorana modes (MMs) localized at the boundaries. In this work, within quasiclassical approximation we study the effect of disorder on the localization length of MMs in two dimensional spin-orbit (SO) coupled superconductors. We find nonmonotonic behavior of the Majorana localization length as a function of disorder strength. At weak disorder, the Majorana localization length decreases with an increasing disorder strength. Decreasing the disorder scattering time below a critical value $τ_c$, the Majorana localization length starts to…
We discuss a mechanism of microwave absorption in conventional superconductors which is similar to the Debye absorption mechanism in molecular gases. The contribution of this mechanism to the \emph{ac} conductivity is proportional to the inelastic quasiparticle relaxation time $τ_\mathrm{\mathrm{in}}$ rather than the elastic one $τ_{\mathrm{el}}$ and therefore it can be much larger than the conventional one. The Debye contribution to the linear conductivity arises only in the presence of a \emph{dc} supercurrent in the system and its magnitude depends strongly on the orientation of the microwa…
We study a chain of magnetic impurities on a conventional superconductor with spin-orbit coupling, treating the superconducting order fully self-consistently. We find and quantify strong hybridization between the topological edge Majorana bound states (MBSs) and in-gap Yu-Shiba-Rusinov (YSR) states, which causes increasing energy oscillations as a function of magnetic impurity strength, even when the direct MBS overlap is negligible. By treating the MBS as a topological boundary state, dependent only on the effective mass gap, we arrive at a fully parameter-free functional form of the its loca…
Recently a generic model has been proposed for the single-particle properties of gapless superconductors with simultaneously present pair-conserving and pair-breaking impurity scattering (the so-called Dynes superconductors). Here we calculate the optical conductivity of the Dynes superconductors. Our approach is applicable for all disorder strengths from the clean up to the dirty limit and for all relative ratios of the two types of scattering, nevertheless the complexity of our description is equivalent to that of the widely used Mattis-Bardeen theory. We identify two optical fingerprints of…
Chiral Optical Absorption by a Vortex in p_x \pm i p_y-Wave Superconductor
本文从理论上研究了p_x \pm i p_y波超导体中单个涡旋的手征光吸收。Sr_2RuO_4超导体的p_x \pm i p_y波态是最近提出的序参量的对称性。由于时间反演对称性的破坏，存在两种类型的涡旋，其缠绕方向与库珀对的角动量相同或相反。在具有p_x的真实材料域中，预计会出现\pm i p_y波状态。然而，圆偏振光的光学吸收仅取决于涡旋的缠绕，并且具有导致二向色性的低能量吸收峰。如果在单个费米面片上实现超导，就会出现二向色性。然而，在几个费米表面片的情况下，二向色性可能会消失，如果这两种类型的载流子都存在，电子类和空穴类。因此，手征光吸收是一个可能的实验来探测Sr_2RuO_4的轨道相关超导性，即超导态。
