Disordered superconductors: Third-harmonic response and charge fluctuations

本项目的科学目的与理解铜超导体中无序对以下方面的影响有关：(a)泵-探针实验中三次谐波响应的集体模式特征。在这里，我们计划研究d波超导体在无序影响下的相应谱。特别是，我们对振幅、电荷和相位模式对低能量响应的贡献感兴趣，我们还打算分析远程库仑相互作用的影响。我们的目的是解释实验观察到的极化依赖以及铜超导体中三次谐波响应的相位，这与s波系统的预期有很大不同。(b)电荷顺序和电荷密度波动的结构。最近的实验表明，在相图的大部分存在短程电荷波动，这可能解释了奇怪金属相中不寻常的输运性质。在目前的项目中，我们打算研究这种波动在无序应变薄膜中的结构，其中输运和RIXS实验已经揭示了向列基态。在这两个主题上，我们与罗马大学物理系的固态理论小组长期合作，我们的目标是在本提案中继续合作。

The scientific aim of the present project is related to an understanding of the influence of disorder in cuprate superconductors with regard to the following aspects:(a) Signatures of collective modes in the third-harmonic response of pump-probe experiments. Here we are planning the investigation of the corresponding spectra for d-wave superconductors under the influence of disorder. In particular, we are interested in the contribution of amplitude- , charge and phase modes on the low energy response where we also intend to analyze the influence of long-range Coulomb interactions. We aim to explain the experimentally observed polarization dependence as well as the phase of the third harmonic response in cuprate superconductors which is substantially different from that expected for s-wave systems.(b) Structure of charge-order and charge density wave fluctuations. Recent experiments have revealed the presence of short-range charge fluctuations in a large part of the phase diagram which may account for the unusual transport properties in the strange metal phase. Within the present project we intend to study the structure of such fluctuations in disordered strained films where transport and RIXS experiments have revealed a nematic ground state.On both topics we have a long-standing cooperation with the Solid State Theory group of the Department of Physics at the University of Rome ’La Sapienza’ which we aim to continue within the present proposal.