Helical superconducting edge modes from pseudo-Landau levels in graphene

螺旋超导体中的超流二极管效应

Supercurrent Diode Effect in Helical Superconductors

本研究以具有Rashba型自旋轨道耦合的二维螺旋相超导体模型为例，结合金兹堡-朗道唯象理论与微观计算探究超流二极管效应，推导效率公式并与准经典近似研究对比。

Pseudo-Landau levels of Bogoliubov quasiparticles in strained nodal superconductors

Motivated by theory and experiments on strain induced pseudo-Landau levels (LLs) of Dirac fermions in graphene and topological materials, we consider its extension for Bogoliubov quasiparticles (QPs) in a nodal superconductor (SC). We show, using an effective low energy description and numerical lattice calculations for a d-wave SC, that a spatial variation of the electronic hopping amplitude or a spatially varying s-wave pairing component can act as a pseudo-magnetic field for the Bogoliubov QPs, leading to the formation of pseudo-LLs. We propose realizations of this phenomenon in the cuprate…

Low energy collective modes, Ginzburg-Landau theory, and pseudogap behavior in superconductors with long-range pairing interactions

We study the superconducting instability in systems with long but finite ranged, attractive, pairing interactions. We show that such long-ranged superconductors exhibit a new class of fluctuations in which the internal structure of the Cooper pair wave function is soft, and thus lead to "pseudogap" behavior in which the actual transition temperature is greatly depressed from its mean field value. These fluctuations are {\it not} phase fluctuations of the standard superconducting order parameter, and lead to a highly unusual Ginzburg-Landau description. We suggest that the crossover between the…

Helical ordering in the ground state of spin-one color superconductors as a consequence of parity violation

We investigate spin-one color superconductivity of a single quark flavor using the Ginzburg-Landau theory. First we examine the classic analysis of Bailin and Love and show that by restricting to the so-called inert states, it misses the true ground state in a part of the phase diagram. This suggests the use of the more general, noninert states in particular within three-flavor quark matter where the color neutrality constraint imposes stress on the spin-one pairing and may disfavor the symmetric color-spin-locked state. In the second part of the paper we show that, in analogy to some ferromag…

Supeconductivity in the Pseudogap State in "Hot - Spots" Model: Ginzburg - Landau Expansion

We analyze properties of superconducting state (for both s-wave and d-wave pairing), appearing on the "background" of the pseudogap state, induced by fluctuations of "dielectric" (AFM(SDW) or CDW) short -- range order in the model of the Fermi surface with "hot spots". We present microscopic derivation of Ginzburg - Landau expansion, taking into account all Feynman diagrams of perturbation theory over electron interaction with this short - range order fluctuations, leading to strong electronic scattering in the vicinity of "hot spots". We determine the dependence of superconducting critical te…

Non-Abrikosov Vortex and Topological Knot in Two-gap Superconductor

We establish the existence of topologically stable knot in two-gap superconductor whose topology $π_3(S^2)$ is fixed by the Chern-Simon index of the electromagnetic potential. We present a helical magnetic vortex solution in Ginzburg-Landau theory of two-gap superconductor which has a non-vanishing condensate at the core, and identify the knot as a twisted magnetic vortex ring made of the helical vortex. We discuss how the knot can be constructed in the recent two-gap $\rm MgB_2$ superconductor.

The pseudogap state in superconductors: Extended Hartree approach to time-dependent Ginzburg-Landau Theory

It is well known that conventional pairing fluctuation theory at the Hartree level leads to a normal state pseudogap in the fermionic spectrum. Our goal is to extend this Hartree approximated scheme to arrive at a generalized mean field theory of pseudogapped superconductors for all temperatures $T$. While an equivalent approach to the pseudogap has been derived elsewhere using a more formal Green's function decoupling scheme, in this paper we re-interpret this mean field theory and BCS theory as well, and demonstrate how they naturally relate to ideal Bose gas condensation. Here we recast the…

螺旋Rashba交换规范场驱动EuRbFe$_4$As$_4$中的单轴配对密度波

Helical Rashba-exchange gauge field drives a uniaxial pair density wave in EuRbFe$_4$As$_4$

针对EuRbFe$_4$As$_4$中零场配对密度波的自发形成机制，本文提出Rashba自旋轨道耦合与螺旋交换场共同产生层旋转有效U(1)规范场，通过轨道选择有限动量配对不稳定性，在Ginzburg-Landau理论框架下自然稳定了单轴Bloch超导态，并预言了层间环流。

Quasiclassical theory of disordered Rashba superconductors

We derive the quasiclassical equations that describe two-dimensional superconductors with a large Rashba spin-orbit coupling and in the presence of impurities. These equations account for the helical phase induced by an in-plane magnetic field, with a superconducting order parameter that is spatially modulated along a direction perpendicular to the field. We also derive the generalized Ginzburg-Landau functional, which includes a linear-in-gradient term corresponding to the helical phase. This theory paves the way for studies of the proximity effect in two-dimensional electron gases with large…

Landau levels from neutral Bogoliubov particles in two-dimensional nodal superconductors under strain and doping gradients

Motivated by recent work on strain-induced pseudo-magnetic fields in Dirac and Weyl semimetals, we analyze the possibility of analogous fields in two-dimensional nodal superconductors. We consider the prototypical case of a d-wave superconductor, a representative of the cuprate family, and find that the presence of weak strain leads to pseudo-magnetic fields and Landau quantization of Bogoliubov quasiparticles in the low-energy sector. A similar effect is induced by the presence of generic, weak doping gradients. In contrast to genuine magnetic fields in superconductors, the strain- and doping…

手性诱导的赝磁场、平带与超导电性增强

Chirality-induced pseudo-magnetic fields, flat bands and enhancement of superconductivity

本文研究手性自旋织构诱导赝磁场对超导的影响，发现Cooper对不受拆对效应阻碍，并提出平Landau能级可显著提高超导转变温度，主导配对态为FFLO型s波配对密度波。

Electromagnetic properties of a Fermi liquid superconductor with singular Landau parameter $F_{1s}\to-1$

The electromagnetic properties of a Fermi liquid superconductor with singular Landau parameter $F_{1s}\to-1$, corresponding to a state with marginal spin-charge separation (MSCS) is analyzed in this paper. We show that the MSCS state describes a strongly phase-disordered superconductor which is a diamagnetic metal with Drude-like optical conductivity. The phase diagram and electromagnetic properties of the MSCS state is found to be in qualitative agreement with what is observed in the pseudo-gap phase of (underdoped) High-$T_c$ cuprates. We predicted that vortices with {\em un-quantized} magne…