Bogoliubov Fermi surfaces in topological superconductors

超导体对于准粒子激发有一个能隙。在非常规超导体中，对于这些准粒子的某些动量，这个能隙可以变为零。这些差距的零点称为节点。我们最近表明，在自发打破时间反演对称性的多带超导体中，这些节点一般是二维的。它们可以被理解为Bogoliubov准粒子的费米面。这是有趣的，因为费米表面通常被认为是正常导体的标志。本项目的主要研究方向有两个：一是在微观基础上研究时间反演破缺对态，二是研究费米面的可能实验特征。本项目第一部分的主要目标是从具有对相互作用的微观模型出发，获得显示Bogolibov费米面的时间反演破缺对态。我们的目标是了解这种配对状态优于传统状态的条件。这些超导状态的空间结构，特别是接近表面，也将被研究。这对于描述表面敏感探针是至关重要的。此外，现在重要的是提出实验探测器，并为它们做出预测。我们的目标是了解如何Bogoliubov费米面和随之而来的磁序影响标准探头的超导状态，特别是光电发射，隧道，热力学量，磁穿透深度，磁化，核探针，和光学电导率。此外，我们有初步的论点，量子振荡应该存在，尽管事实上，博戈留波夫准粒子是电中性的平均。对于所有的量，我们将阐明它们对温度和外加磁场的依赖关系，这预计是特征的配对状态和Bogoliubov费米面。

Superconductors have an energy gap towards quasiparticle excitations. In unconventional superconductors, this gap can go to zero for certain momenta of these quasiparticles. These zeros of the gap are called nodes. We have recently shown that in multiband superconductors that spontaneously break time-reversal symmetry, these nodes are generically two dimensional. They can be understood as Fermi surfaces of Bogoliubov quasiparticles. This is interesting since Fermi surfaces are typically thought of as a hallmark of normal conductors. Two directions of research are now pressing and will be pursued in this project: the time-reversal-symmetry-breaking pairing states have to be put on a microscopic basis and possible experimental signatures of the Fermi surfaces have to be worked out.The main objective in the first part of this project is to obtain time-reversal-symmetry-breaking states that show Bogolibov Fermi surfaces starting from microscopic models with a pairing interaction. The goal is to understand the conditions for such pairing states to be favored over conventional ones. The spatial structure of these superconducting states, in particular close to a surface, will also be studied. This is crucial for the description of surface-sensitive probes. Furthermore, it is now important to suggest experimental probes and to derive predictions for them. Our goal is to understand how the Bogoliubov Fermi surfaces and the concomitant magnetic order affect standard probes of superconducting states, in particular photoemission, tunneling, thermodynamic quantities, the magnetic penetration depth, the magnetization, nuclear probes, and the optical conductivity. Moreover, we have preliminary arguments that quantum oscillations should exist in spite of the fact that the Bogoliubov quasiparticles are electrically neutral on average. For all quantities, we will elucidate their dependences on temperature and applied magnetic field, which are expected to be characteristic for the pairing state and the Bogoliubov Fermi surfaces.