Recent experimental progress in the fields of cold quantum gases and ultrafast optical spectroscopy of quantum materials allows to controllably induce and probe non-adiabatic dynamics of superconductors and superfluids. The time-evolution of the gap function before relaxation with the lattice is determined by the superposition of coherently evolving individual Cooper pairs within the manifold of the Bardeen-Cooper-Schrieffer (BCS) wavefunction. While dynamics following an abrupt quench of the pairing interaction strength in the single-band BCS model has been exactly solved due to the integrability of the model, the dynamics of post-quench multi-band superconductors remain under scrutiny. Here, we develop a generalization of the Volkov-Kogan Laplace-space perturbative method that allows us to determine the non-adiabatic gap dynamics of two-band fully gapped superconductors for a wide range of quench amplitudes. Our approach expands the long-time dynamics around the steady-state asymptotic value of the gap, which is self-consistently determined, rather than around the equilibrium value of the gap. We explicitly demonstrate that this method recovers the exact solution of the long-time gap dynamics in the single-band case and perfectly agrees with a numerical solution of the two-band model. We discover that dephasing of Cooper pairs from different bands leads to faster collisionless relaxation of the gap oscillation with a power-law of $t^{-3/2}$ instead of the well-known $t^{-1/2}$ behavior found in the single-band case. Furthermore, the gap oscillations display beating patterns arising from the existence of two different asymptotic gap values. Our results have important implications to a variety of two-band superconductors driven out of equilibrium, such as iron-based superconductors, MgB$_{2}$, and SrTiO$_{3}$.
Ultrafast carrier localisation in the pseudogap state of cuprate superconductors from coherent quench experiments
赝能隙（PG）是由莫特引入的，用来描述一种物质状态，这种状态在费米能级上具有最小的态密度，深到足以使态局域化。它可以由电子之间的库仑排斥引起，或者由于初始电荷或自旋序，或者两者的组合。这些状态在时间上以随机相位快速波动，因此很难在实验上观察到。在这里，我们提出了第一个相干淬火测量的原型高温超导体Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$中的赝能隙态的动态过渡，揭示了一个显着的早期集体秩序在短时间尺度上超过几个相干长度在任何水平的掺杂。相反，我们发现亚皮秒载波本地化的证据有利于图片的配对竞争库仑相互作用和应变，增强了费米表面的不稳定性。
Periodic dynamics in superconductors induced by an impulsive optical quench
许多实验已经证明了光激发后增强的超导关联的签名。最初，这些实验被解释为由于准静态变化的哈密顿参数，例如，由于晶格变形或熔化的竞争相。然而，最近的几次观测表明，这些结构要么是不正确的，要么没有捕捉到所有观察到的现象，包括反射率超过1，约瑟夫森等离子体边缘的大位移，以及太赫兹反射率出现新的峰值。这些观测结果可以从Floquet理论的角度来解释，该理论涉及系统参数的周期性驱动，但潜在振荡的起源仍不清楚。在本文中，我们表明，以下的非相干光激发，长寿命的振荡通常预计在超导体与低能量约瑟夫森等离子体，如铜酸盐或富勒烯超导体K $_3$ C $_{60}$。这些振荡产生的等离子体激元对由于泵引起的超导序参量扰动的参数生成。我们表明，这种双等离子体激元响应可以持续甚至高于转变温度，只要存在强超导波动。我们的分析提供了一个强大的框架来理解光致超导行为，预测的双等离子体激元振荡可以直接检测使用现有的实验技术。
Enhanced charge density wave coherence in a light-quenched, high-temperature superconductor
在铜氧化物超导体中，超导性和电荷密度波（CDW）是相互竞争但又共存的有序现象。为了理解它们的微观相互依赖性，需要一种能够在自然长度和时间尺度上识别它们相互作用的探针。我们用超快共振软X射线散射跟踪CDW关联在YBaPDMATHABMM CuPDMATHABMN O $_{6+x}$中的瞬态演化。我们观察到的非热响应的CDW顺序的特点是近一倍的相关长度内$\approx$ 1皮秒的超导淬火。我们的研究结果是一致的模型，其中超导性和CDW之间的相互作用，通过破坏空间相干性表现为不均匀的，超导性发挥主导作用，稳定CDW拓扑缺陷，如dispersiations。
Quenched nematic criticality separating two superconducting domes in an iron-based superconductor under pressure
电子态及其相关的临界涨落已经成为各种非常规超导体中超导配对的潜在候选者。然而，在大多数材料中，它们与其他磁有序相的共存对确定它们的重要性提出了重大挑战。在这里，通过结合化学和流体静力学的物理压力在FeSe $_{0.89}$ S $_{0.11}$，我们提供了一个独特的访问一个干净的量子相变的情况下的远程磁秩序。我们发现在超导相变附近，高温下电阻率的非费米液体行为在最低温度下演变为费米液体行为。从高磁场中的量子振荡，我们跟踪费米面和电子关联的演化作为施加压力的函数。我们检测实验的Lifshitz过渡，分离两个不同的超导区域：一个新兴的电子相位与一个小的费米面和强电子相关性和其他一个大的费米面和弱相关性，促进嵌套和稳定的磁有序相在高压下。质量发散的缺乏表明临界涨落被晶格的强耦合淬灭。这表明在没有磁序的情况下，超导性在量子相变时不会增强。
Interpretation of experimental Critical Current Density and Levitation of Superconductors, and a second Temperature Limit to protect Superconductors against Quench
