Type-1.5 superconductivity in multiband systems: Effects of interband couplings
Type-1.5 superconductivity in multiband systems: Effects of interband couplings
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DOI：
10.1103/physrevb.83.174509
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发表时间：
2010-09
影响因子：
3.7
通讯作者：
J. Carlstrom;E. Babaev;Martin Speight
中科院分区：
文献类型：
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作者：
J. Carlstrom;E. Babaev;Martin Speight
本论文的题目是多分量Ginzburg-朗道模式中的涡旋物理。这些模型描述了一类新发现的具有多个超导间隙的超导体，并且具有许多使它们与单组分模型区分开的性质。本文的工作依赖于使用各种数值技术的大规模计算机模拟，但也依赖于一些分析方法.在论文I，Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors中，我们表明，在多带超导体中，即使是极小的带间邻近效应也能导致超导涡旋之间相互作用势的质的变化，通过产生远距离的漩涡间吸引力这种类型的涡旋相互作用导致对低磁场的不寻常响应，导致相分离成两组分迈斯纳态和涡旋液滴的域。我们讨论了约瑟夫森耦合的影响，并表明，非单调涡间相互作用也可以出现在两个-带超导体，其中一个带是由约瑟夫森带间耦合引起的邻近。在论文III中，多带系统中的1.5型超导性：带间耦合的影响，我们研究了在两个激活带和大量的带间耦合，如本征约瑟夫森耦合，混合梯度耦合，和密度-密度的相互作用。我们证明了在这些相互作用的存在下，系统支持1.5型超导，其基本长度尺度与规范场的质量和由密度场的线性组合表示的两个正常模的质量有关.在论文IV中，1.5型超导体中的半迈斯纳态和非成对涡旋间相互作用，我们证明了在多组分和层状超导系统中存在非成对的互涡旋力。我们还考虑了1.5型双组分超导体半迈斯纳态中涡旋团簇的性质。我们证明了在一定条件下，非成对力可以促成1.5型区域中复杂涡旋态的形成.在论文V，三带超导体中的长度尺度、集体模和1.5型区域中，我们考虑了由于竞争约瑟夫森带间耦合项而导致相位差受挫的系统.我们发现，密度和相位差的梯度可以不可避免地交织在三带模型中的涡旋激发。这可能会导致长距离的吸引力涡间相互作用和外观的类型-1.5制度，即使当组件间的约瑟夫森耦合是大的。我们还发现，场诱导涡旋可以导致系统的对称性破缺从U（1）到U（1）<$Z ~ 2的变化。在Type-1.5区域，它导致了一个半Meissner态，此时系统在U（1）和U（1）→ Z ~ 2对称性破缺的区域内存在宏观相分离.在论文VI，时间反演对称性破缺的三带超导体中的拓扑孤子，我们证明了时间反演对称性破缺的三带超导体中存在携带磁通量的稳定拓扑孤子.它们可以由涨落或通过相变猝灭系统引起。它可以提供一个实验签名的时间反演对称breakdown.In文件VII，类型-1.5超导多带系统：磁响应，对称性破缺和微观理论-一个简要的概述，我们给出了一个概述的涡旋物理和磁响应多分量金斯堡-朗道理论。我们还研究了1.5型超导的微观theory.In文件VIII，手征CP 2 skyrmions在三带超导体的背景下，我们表明，在一定条件下，三组分超导体（和，特别是，三带系统）允许稳定的拓扑缺陷不同的涡旋。我们证明了这些激发的存在，charac- terised由CP 2拓扑不变量，在模型中的三组分超导体与破缺的时间反演对称性。我们称这些拓扑缺陷为“手征GL（3）skyrmions”，其中“手征”指的是由于时间反演对称性破缺，这些缺陷以不等价的左手和右手形式出现。在某些情况下，这些物体在能量上比涡流便宜，应该由施加的磁场引起。在其他情况下，这些skyrmions是亚稳态，可以通过淬火产生。在三带超导体或约瑟夫森耦合的s±和s波超导体双层中，对这些缺陷的观测可以表明时间反演对称性的破坏。在论文IX，多组分超导体中的相变，我们研究了阻挫多组分超导体的热力学，并表明它们高度复杂的能量景观可以引起单组分超导体中不存在的新类型的相变。
The topic of this thesis is vortex-physics in multi component Ginzburg- Landau models. These models describe a newly discovered class of super- conductors with multiple superconducting gaps, and possess many properties that set them apart from single component models. The work presented here relies on large scale computer simulations using various numerical techniques, but also on some analytical methods.In Paper I, Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors, we show that in multiband supercon- ductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vor- tices, by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response to low magnetic fields, leading to phase separation into domains of two-component Meissner states and vortex droplets.In paper II, Type-1.5 superconductivity in two-band systems, we discuss the influence of Josephson coupling and show that non-monotonic intervortex interaction can also arise in two-band superconductors where one of the bands is proximity induced by Josephson interband coupling.In paper III, Type-1.5 superconductivity in multiband systems: Effects of interband couplings, we investigate the appearance of Type-1.5 superconduc- tivity in the case with two active bands and substantial inter-band couplings such as intrinsic Josephson coupling, mixed gradient coupling, and density- density interactions. We show that in the presence of these interactions, the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by linear combinations of the density fields.In paper IV, Semi-Meissner state and nonpairwise intervortex interactions in type-1.5 superconductors, we demonstrate the existence of nonpairwise in- tervortex forces in multicomponent and layered superconducting systems. We also consider the properties of vortex clusters in a semi-Meissner state of type- 1.5 two-component superconductors. We show that under certain conditions nonpairwise forces can contribute to the formation of complex vortex states in type-1.5 regimes.In paper V, Length scales, collective modes, and type-1.5 regimes in three- band superconductors, we consider systems where frustration in phase dif- ferences occur due to competing Josephson inter-band coupling terms. We show that gradients of densities and phase differences can be inextricably intertwined in vortex excitations in three-band models. This can lead to long-range attractive intervortex interactions and the appearance of type-1.5 regimes even when the intercomponent Josephson coupling is large. We also show that field-induced vortices can lead to a change of broken symmetry from U (1) to U (1) ⇥ Z2 in the system. In the type-1.5 regime, it results in a semi-Meissner state where the system has a macroscopic phase separation in domainswithbrokenU(1)andU(1)⇥Z2 symmetries.In paper VI, Topological Solitons in Three-Band Superconductors with Broken Time Reversal Symmetry, we show that three-band superconductors with broken time reversal symmetry allow magnetic flux-carrying stable topo- logical solitons. They can be induced by fluctuations or quenching the system through a phase transition. It can provide an experimental signature of the time reversal symmetry breakdown.In paper VII, Type-1.5 superconductivity in multiband systems: Magnetic response, broken symmetries and microscopic theory – A brief overview, we give an overview of vortex physics and magnetic response in multi component Ginzburg-Landau theory. We also examine Type-1.5 superconductivity in the context of microscopic theory.In paper VIII, Chiral CP2 skyrmions in three-band superconductors, we show that under certain conditions, three-component superconductors (and, in particular, three-band systems) allow stable topological defects different from vortices. We demonstrate the existence of these excitations, charac- terised by a CP2 topological invariant, in models for three-component super- conductors with broken time-reversal symmetry. We term these topological defects “chiral GL(3) skyrmions,” where “chiral” refers to the fact that due to broken time-reversal symmetry, these defects come in inequivalent left- and right-handed versions. In certain cases, these objects are energetically cheaper than vortices and should be induced by an applied magnetic field. In other situations, these skyrmions are metastable states, which can be produced by a quench. Observation of these defects can signal broken time-reversal sym- metry in three-band superconductors or in Josephson-coupled bilayers of s± and s-wave superconductors.In paper IX, Phase transition in multi-component superconductors, we ex- amine the thermodynamics of frustrated multi-components superconductors and show that their highly complex energy landscape can give rise new types of phase transitions not present in single component superconductors.