Magnetic field induced 3D to 1D crossover in type II superconductors
T. Schneider
我们回顾和分析了II型超导体的磁化和比热研究，发现了磁场诱导的有限尺寸效应和相关的3D到1D交叉，增强热波动的显着证据。
We review and analyze magnetization and specific heat investigations on type-II superconductors which uncover remarkable evidence for the magnetic field induced fnite size effect and the associated 3D to 1D crossover which enhances thermal fluctuations.
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Superconductor-Metal-Insulator Crossover in Disordered Thin Films
本文在随机结网络模型的基础上讨论了无序薄膜中的超导体-金属-绝缘体交叉。
Dimensional crossover of the thermodynamic properties near the phase transition to superconducting state in type I superconductors
本文介绍了一种处理I型超导体薄膜中磁起伏的新方法。得到了平衡相变点附近自由能、比热和序参量分布随膜厚变化的结果，并进行了讨论。
Dimensional Crossover in Quasi One-Dimensional and High T_c Superconductors
一维电子气表现出自旋电荷分离和幂律光谱响应许多实验相关的探针。准一维系统中的有序化必然伴随着一个维度交叉，在这个维度交叉处，具有小光谱权重的尖锐准粒子峰从非相干背景中出现。使用阿贝尔玻色化的方法，我们推导出渐近正确的表达式，这种交叉引起的光谱变化。与高温超导体的实验结果作了比较，这些超导体在局域尺度上是电子准一维的。
Based on a simple model of a layered superconductor with strong attractive interaction, we find that the separation of the pair-condensation temperature from the pair-formation temperature becomes more remarkable as the interlayer hopping gets smaller. We propose from this result the BCS-BEC crossover induced by the change in dimensionality, for instance, due to insertion of additional insulating layers or application of uniaxial pressure. The emergence of a pseudogap in the electronic density of states, which supports the idea of the dimensionality-induced BCS-BEC crossover, is also verified.
Crossover from thermal to quantum creep in layered antiferromagnetic superconductor
反铁磁序对混合态超导体的影响导致沿涡旋线核心产生自旋翻转畴。结果表明，这种现象使得在恒定温度下，量子蠕变区和热蠕变区之间的交叉成为可能。为此，需要简单地改变在层状结构的基底${\bf ab}$平面中施加的磁场的强度或方向。
1D to 3D Dimensional Crossover in the Superconducting Transition of the Quasi-One-Dimensional Carbide Superconductor Sc3CoC4
过渡金属碳化物超导体Sc_3CoC_4可能代表准一维超导行为的新基准体系。通过电输运实验研究了高质量单晶样品的超导转变。我们的数据表明，超导体通过一个复杂的维度交叉低于4.5 K的起始Tc。首先，一个准一维波动超导态的有限电阻的形式在CoC4带，这是嵌入在一个Sc矩阵在这种材料中。在较低的温度下，相邻带的横向约瑟夫森或邻近耦合建立了3D体超导态。这种维度交叉与Tl_2Mo_6Se_6非常相似，Tl_2Mo_6Se_6长期以来一直被认为是准一维超导体的最合适的模型系统。Sc3CoC4似乎比Tl2Mo6Se6更接近一维极限。
The Bardeen-Cooper-Schrieffer (BCS) condensation and the Bose-Einstein condensation (BEC) are the two extreme limits of the ground state of the paired fermion systems. We report crossover behavior from the BCS condensation to the BEC realized in the two-dimensional (2D) superconductor, electron doped layered material ZrNCl. The phase diagram, established by simultaneous experiments of resistivity and tunneling spectra under the ionic gating, demonstrates the pseudogap phase at the low doping regime. In the low carrier density limit, $T_{\rm BKT}$ (Berezinskii-Kosterlitz-Thouless transition tem…
We report a nontrivial transition in the core structure of vortices in two-band superconductors as a function of interband impurity scattering. We demonstrate that, in addition to singular zeros of the order parameter, the vortices there can acquire a circular nodal line around the singular point in one of the superconducting components. It results in the formation of the peculiar "moat"-like profile in one of the superconducting gaps. The moat-core vortices occur generically in the vicinity of the impurity-induced crossover between $s_{\pm}$ and $s_{++}$ states.
Band-edge BCS-BEC crossover in a two-band superconductor: physical properties and detection parameters
铁基、硼化镁等新型超导材料的超导性具有很强的多带和多能隙特性。最近的实验支持的BCS-BEC交叉诱导的强耦合和接近的化学势的带边的一个频带的可能性。在这里，我们研究了最简单的理论模型，考虑到可调的相互作用和可调的能带之间的能量分离的BCS-BEC交叉在一个两带超导体。在典型的交叉图中报告了凝结分数、相关长度和超导能隙的平均场结果，以确定BCS、交叉和BEC制度的边界。当超导能隙为局域化学势量级时，超导处于BCS-BEC交叉区，小能带的费米面被能隙开口所模糊。在这种情况下，小的和大的库珀对共存的总凝聚，这是高Tc超导的最佳条件。在给定的频带中的间隙和费米能量之间的比率的结果是最好的检测参数的实验定位系统中的BCS-BEC交叉。利用现有的实验数据，我们的分析表明，铁基超导体具有的BCS-BEC交叉的交叉制度的小费米面的部分冷凝，支持最近的ARPES的结果。
Ultranarrow superconductors are in the strong quantum confinement regime with formation of multiple coherent condensates associated with the many subbands of the electronic structure. Here we analyze the multiband BCS-BEC crossover induced by the chemical potential tuned close to a subband bottom, in correspondence of a superconducting shape resonance. The evolution of the condensate fraction and of the pair correlation length in the ground state as functions of the chemical potential demonstrates the tunability of the BCS-BEC crossover for the condensate component of the selected subband. The…
Test for BCS-BEC Crossover in the Cuprate Superconductors
本文提出通过测量金兹堡-朗道相干长度ξ₀^{coh}在T_c附近及整个超导穹顶的行为，为铜氧化物高温超导体是否适用BCS-BEC渡越理论提供具体检验，并激励相关实验。
Hidden Crossover Phenomena in Strongly Pauli Limited Multiband Superconductors ---Application to CeCu$_2$Si$_2$
基于最近对重费米子材料CeCu $_2$ Si $_2$和UBe $_{13}$的实验研究，我们建立了一个框架来描述具有强泡利顺磁效应（PPE）的多带超导体的一般性质.与单带情况相比，即使在强PPE情况下，上临界场$H_{\rm c2}$仍能保持二级跃迁。预期的一阶跃迁隐藏在$H_{\rm c2}$内部，并由于多频带的相互作用而成为交叉。本文基于微观Eilenberger理论的完全自洽解，解释了最近在CeCu $_2$ Si $_2$上的STM实验中观察到的与交叉和“空”涡核态有关的几种神秘异常现象。
In this review article we consider theoretically and give experimental support to the models of the Fermi-Bose mixtures and the BCS-BEC crossover compared with the strong-coupling approach, which can serve as the cornerstones on the way from high-temperature to room-temperature superconductivity in pressurized metallic hydrides. We discuss some key theoretical ideas and mechanisms proposed for unconventional superconductors (cuprates, pnictides, chalcogenides, bismuthates, diborides, heavy-fermions, organics, bilayer graphene, twisted graphene, oxide hetero-structures), superfluids and balance…
Magnetic-field tuned superconductor to insulator transition was observed in a novel hybrid system of granular superconducting indium, deposited on indium oxide thin film, which exhibits global superconductivity at low magnetic fields. We have used annealing to tune the coupling to lie just at the borderline where superconductivity in the underlying InOx is suppressed, which is also close to the metal-insulator transition of the InOx. The hybrid system exhibits a "giant" magnetoresistance above the H-SIT, with critical behavior that manifests the duality between Cooper pairs and vortices.
Crossover from hc/e to hc/2e current oscillations in rings of s-wave superconductors
我们分析了从一个HC/E-周期性的持续电流在磁通线程清洁金属环对HC/2 E-磁通周期性的超导进入超导状态时的交叉。一维环的模型计算的基础上，我们确定的基本机制，它平衡的HC/E与HC/2 E的电流密度的周期分量。当环的周长超过超导体的相干长度时，磁通依赖性是严格的hc/2 e周期。此外，我们开发了一个多通道模型，它减少了Bogoliubov - de Gennes方程的径向分量的波函数的一维微分方程。该微分方程的离散化引入了横向通道，其数量与环的厚度成比例。在临界温度附近分析了周期性交叉。
Absence of a BCS-BEC crossover in the cuprate superconductors
本文通过分析化学势的温度依赖性，证明铜氧化物超导体始终处于BCS侧，远离BCS-BEC渡越点，不存在该渡越现象。
Bulk-edge correspondence at the spin-to-integer quantum Hall effect crossover in topological superconductors
该研究探讨二维拓扑超导体中，通过增强塞曼磁场实现自旋到整数量子霍尔效应转变时，体边对应及无质量边缘和瞬子激发的行为。
Crossovers and Phase Coherence in Cuprate Superconductors
高温超导性是掺杂反铁磁绝缘体的一种性质。电子结构在短的长度和时间尺度上是不均匀的，并且随着温度的降低，它通过两个交叉演变，在实现长程超导有序之前。除了过掺杂的材料，配对和相位相干性发生在不同的温度下，和相位波动确定T $_c$和温度依赖性的超流密度为广泛的掺杂。描述了一种在具有强的弱屏蔽库仑相互作用的短相干长度材料中获得高配对尺度的机制。
Evidence of Strong Correlations and Coherence-Incoherence Crossover in the Iron Pnictide Superconductor KFe2As2
使用电阻率，热容量，热膨胀，和磁化率测量，我们研究了正常状态下的行为KFe 2As 2。我们发现索末菲系数γ = 103 mJ mol-1 K-2和泡利磁化率chi = 4 × 10 -4都得到了强烈的增强，这证实了由de Haas-van Alphen和ARPES实验推断的重准粒子的存在。我们讨论这个大的增强使用Gutzwiller从玻色子平均场计算，揭示了接近KFe 2As 2的轨道选择性莫特过渡。由于Hund轨道之间的耦合，磁化率和热膨胀的温度依赖性为相干-非相干交叉的存在提供了强有力的实验证据，类似于在重费米子和钌酸盐化合物中发现的情况。
The recently discovered kagome superconductors AV3Sb5 exhibit tantalizing high-pressure phase diagrams, in which a new dome-like superconducting phase emerges under moderate pressure. However, its origin is as yet unknown. Here, we carried out the high-pressure electrical measurements up to 150 GPa, together with the high-pressure X-ray diffraction measurements and first-principles calculations on CsV3Sb5. We find the new superconducting phase to be rather robust and inherently linked to the interlayer Sb2-Sb2 interactions. The formation of Sb2-Sb2 bonds at high pressure tunes the system from …
3D-2D crossover in the naturally layered superconductor (LaSe)1.14(NbSe2)
电阻性上临界磁场$B_{c2}$的温度和角度依赖性揭示了高各向异性失配层单晶（LaSe）$_{1.14}$（NbSe $_2$）超导态的维度交叉，其临界温度$T_c$为1.23 K.沿导电$(ab)$ -平面的场取向的上临界场$B_{c2\parallel ab}(T)$的温度依赖性在1.1 K处显示出特征性的上弯，并且低于该温度时，$B_{c2}$的角度依赖性在平行场取向周围具有尖点。这两个典型的功能是第一次观察到在一个自然的结晶层状系统。
The Bardeen-Cooper-Schrieffer (BCS) condensation and Bose-Einstein condensation (BEC) are the two limiting ground states of paired Fermion systems, and the crossover between these two limits has been a source of excitement for both fields of high temperature superconductivity and cold atom superfluidity. For superconductors, ultra-low doping systems like graphene and LixZrNCl successfully approached the crossover starting from the BCS-side. These superconductors offer new opportunities to clarify the nature of charged-particles transport towards the BEC regime. Here we report the study of vort…
In this paper we present predictions for thermodynamic and transport properties of a BCS Bose-Einstein crossover theory, below Tc, which theory satisfies the reasonable constraints that it yield (i) the Leggett ground state and (ii) BCS theory at weak coupling and all temperatures. The nature of the strong coupling limit is inferred, along with the behavior of the Knight shift, superfluid density, and specific heat. Comparisons with existing data on short coherence length superconductors, such as organic and high Tc systems, are presented, which provide some support for the present picture.
Disorder can have remarkably disparate consequences in superconductors, driving superconductor-insulator transitions in ultrathin films by localizing electron pairs and boosting the supercurrent carrying capacity of thick films by localizing vortices (magnetic flux lines). Though the electronic 3D-to-2D crossover at material thicknesses $d \sim ξ$ (coherence length) is well studied, a similarly consequential magnetic crossover at $d \sim L_c$ (pinning length) that should drastically alter material properties remains largely underexamined. According to collective pinning theory, vortex segments…
In paired Fermi systems, strong many-body effects exhibit in the crossover regime between the Bardeen-Cooper-Schrieffer (BCS) and the Bose-Einstein condensation (BEC) limits. The concept of the BCS-BEC crossover, which is studied intensively in the research field of cold atoms, has been extended to condensed matters. Here, by analyzing the typical superconductors within the BCS-BEC phase diagram, we find that FeSe-based superconductors are prone to shift their positions in the BCS-BEC crossover regime by charge doping or substrate substitution, since their Fermi energies and the superconductin…
Long-range order in quasi-one-dimensional (q1D) arrays of superconducting nanowires is established via a dimensional crossover from a fluctuating 1D regime to a phase-coherent 3D ground state. If a homogeneous crystalline superconductor exhibits sufficiently high uniaxial anisotropy, a similar 1D$\rightarrow$3D crossover has been predicted to occur, provided that single-particle hopping transverse to the 1D axis is absent in the normal state. Here we present magnetic penetration depth and electrical transport data in single crystals of q1D Tl$_2$Mo$_6$Se$_6$, which reveal a 1D$\rightarrow$3D s…
Crossover from weak to strong pairing in unconventional superconductors
超导体是根据它们的配对机制和耦合强度来分类的，耦合强度是以能隙与临界温度的比率Tc来测量的。我们提出了一个广泛的比较的间隙比之间的许多单带和多带超导体从简单的金属到高Tc的铜酸盐和铁pnictides。相反，最近建议的普遍性，这一比例在铁基超导体，我们发现，在pnictides耦合范围从弱，接近BCS限制，到强，在铜酸盐，桥接这两个极端之间的差距。此外，对于Fe基和Cu基材料，我们的分析揭示了间隙比和Tc之间的普遍相关性，这在传统超导体中没有发现，因此支持两个家族中常见的非常规配对机制。一个重要的后果，这一结果的铁磷族化合物是激子自旋共振模式和粒子-空穴连续体之间的能量分离，这决定了共振阻尼，不再出现独立的Tc。
Effective action for Superconductors and BCS-Bose crossover
利用平均场解附近的标准微扰展开式导出了T=0时超导体的低能有效作用量。考虑到密度涨落的影响，我们得到了有效作用量，其中密度$ρ$是序参量的相位$θ$的共轭动量。在流体动力学区域，超导体的动力学由场$Ψ(x)=\sqrt{ρ/2} e^{iθ}$的含时非线性薛定谔方程（TDNLS）描述。本文讨论了在有吸引力的哈伯德模型下，从弱耦合（BCS）到强耦合（局域对的玻色凝聚）超导过渡中密度涨落的演化。在玻色子极限下，TDNLS方程简化为序参量的Gross-Pitaevskii方程，就像超流性的标准描述一样。讨论了在长程相互作用的存在下，可以导出纯相作用来描述"坏金属“的超导性的物理学的条件。
To decipher the mechanism of high temperature superconductivity, it is important to know how the superconducting pairing emerges from the unusual normal states of cuprate superconductors, including pseudogap, anomalous Fermi liquid and strange metal (SM). A long-standing issue under debate is how the superconducting pairing is formed and condensed in the SM phase because the superconducting transition temperature is the highest in this phase. Here, we report the first experimental observation of a pressure-induced crossover from two- to three-dimensional superconducting states in the optimally…
Superconductivity mostly appears in high carrier density systems and sometimes exhibits common phase diagrams in which the critical temperature Tc continuously develops with carrier density. Superconductivity enhanced in lightly doped regime has seldom been reported, although it is an ideal direction towards the crossover between Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensate (BEC) limits, where the behavior of Cooper pairs changes dramatically. Here we report transport properties and superconducting gaps in single-crystalline lithium-intercalated layered nitrides (LixHfNCl and L…
Electron pairing and evidence of a BCS-BEC crossover in d-wave superconductors
通过数值求解Bogoliubov-de Gennes（BdG）方程组，我们证明了在t-J-U模型描述的二维系统中，当交换相互作用被调谐时，从弱耦合d波超导体到强耦合玻色-爱因斯坦凝聚体（BEC）相的交叉是可能的.而在极稀极限下，电子配对现象与库仑斥力U无关，超导电性依赖于U，交叉也依赖于U。此外，还研究了载流子密度的变化对BCS-BEC交叉的影响。交叉图片说明计算的化学势，当低于非相互作用带的最小值，信号的发病阶段与紧密结合，较短的对。作为上述特征的证据，计算了库珀对半径，其显示在BEC样相出现时显著缩短。此外，与以前的工作相比，交叉声称只在稀释极限，我们已经证明了它在大密度接近半填充。
In type-II superconductors exposed to magnetic fields between upper and lower critical values, $H_{c1}$ and $H_{c2}$, penetrating magnetic flux forms a lattice of vortices whose motion can induce dissipation. Consequently, the magnetization $M$ of superconductors is typically progressively weakened with increasing magnetic field $B \propto n_v$ (for vortex density $n_v$). However, some materials exhibit a non-monotonic $M(B)$, presenting a maximum in $M$ at what is known as the second magnetization peak. This phenomenon appears in most classes of superconductors, including low $T_c$ materials,…
The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally-invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is al…
The crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose-Einstein condensation (BEC) is difficult to realize in quantum materials because, unlike in ultracold atoms, one cannot tune the pairing interaction. We realize the BCS-BEC crossover in a nearly compensated semimetal Fe$_{1+y}$Se$_x$Te$_{1-x}$ by tuning the Fermi energy, $ε_F$, via chemical doping, which permits us to systematically change $Δ/ ε_F$ from 0.16 to 0.5 were $Δ$ is the superconducting (SC) gap. We use angle-resolved photoemission spectroscopy to measure the Fermi energy, the SC gap and characteristic chang…
Absence of BCS-BEC Crossover in FeSe0.45Te0 55 Superconductor
本研究利用高分辨率角分辨光电子能谱技术，分离并研究了FeSe0.45Te0.55超导体中dyz能带与拓扑表面态能带的超导行为，揭示了类平带特征的起源，从而排除了该体系中存在BCS-BEC交叉的可能性。
Comment on ``BCS to Bose-Einstein crossover phase diagram at zero temperature for a d_{x^2-y^2} order parameter superconductor: Dependence on the tight-binding structure''
Soares等人的工作[Phys.Rev.B65，174506（2002）]研究了二维吸引哈伯德模型中d波配对的BCS-BE交叉。与他们的说法相反，我们发现在密度与耦合相图中不存在非配对区域。在T=0的间隙参数，通过解析以及数值求解BCS方程，实际上是有限的任何非零密度和耦合，即使在弱耦合制度。
BEC, BCS and BCS-Bose Crossover Theories in Superconductors and Superfluids
对于超导体中的Cooper/BCS模型相互作用，表明：a）由能隙方程和费米子数方程自洽定义的BCS-玻色交叉图转变温度Tc，由于假定化学势等于费米子能，因而需要非物理的大耦合，才能与没有数方程定义的BCS理论的Tc有显著的差别;尽管在最近的“完全玻色子-费米子模型”中忽略了空穴-或电子-库珀对，但如何：b）人们获得了所有温度T的精确BCS能隙方程，但c）只有一半的零温度BCS凝聚能出现。预计结果（b）和（c）也适用于中性费米子超流体（SF）-例如液体$^3$ He，中子物质和捕获的超冷费米子原子气体-其中成对形成的两个费米子相互作用当然不同于SC的Cooper/BCS。
Groundstate properties of the BCS-Bose Einstein crossover in a $d_{x^{2}-y^{2}}$ wave superconductor
本文研究了具有$d_{x^{2} - y^{2}}$配对对称性的BCS超导与玻色-爱因斯坦凝聚交叉的基态性质。我们比较零温度与已知的s波系统的功能的结果，并表明玻色子的自由度可能只出现在稀释的限制。我们将基态的性质作为密度的函数的不相容原理的效果的变化，并表明，一个粒子的分布函数发生显着变化时，玻色行为出现。
Possibility of BCS-BEC crossover in $κ$-type organic superconductors
针对强关联电子系统中BCS-BEC crossover的实现问题，理论研究κ-HgBr的扩展哈伯德模型，发现其因非化学计量Hg成分和几何阻挫无竞争相，是BCS-BEC crossover候选材料，且其他κ型有机超导体经能带填充和几何阻挫调节也有潜力。
We study LiFeP, LiFeAs and NaFeAs in their paramagnetic metallic phase including dynamical electronic correlations within a density functional theory + slave-spin mean-field framework. The three compounds are found to lie next to the crossover between a normal and a Hund's metal, where a region of enhanced electronic compressibility that may boost superconductivity is systematically present in this type of systems. We find that LiFeP lies in the normal metallic regime, LiFeAs at the crossover, and NaFeAs is in the Hund's metal regime, which possibly explains the different experimental trends f…
Crossover of the pairing symmetry from $s$- to $d$-wave in iron pnictide superconductors
凝聚态物理学的一个重要主题是关联电子系统中的非常规超导性。库珀对的对称结构被认为是理解其超导电性配对机制的关键。在铁磷属元素化物超导体中，序参量的精确对称性及其随掺杂的演化仍然存在很大争议。关于铁基超导体中的配对性质，目前还没有普遍的共识，只留下了从$s^{++}$波到$s^{\pm}$和$d$波的观点。在这里，我们表明，掺杂诱导的对对称性的突然变化，从$s^{++}$ -$d$ -波在BaFe $_{2-x}$ Ni $_{x}$作为$_{2}$系统与$s^{\pm}$状态附近的交叉边界在$x=0.15$。$s^{\pm}$态的存在具有特别的科学意义，因为当$s$波和$d$波的相位一起干涉时，中间相位破坏了配对对称性。对于$x <$ 0.15，伦敦穿透深度的温度依赖性，较低的临界场，和在超导（SC）状态的比热提供了强有力的证据，两个波段的$s$波序参数。掺杂$x >$ 0.15后，我们发现温度和磁场的贡献，在$T^{2}$和$\sqrt{H}$的比热，分别表示线节点的SC间隙。这些发现，从而澄清的对称性，以及SC序参量的演变与掺杂的磷属元素化物超导体。
Spin-singlet Cooper pairs consisting of two electrons with opposite spins cannot directly penetrate from a superconductor to a half-metal (fully spin polarized ferromagnets) which blocks the superconducting proximity effect between these materials. In this paper we demonstrate that, nevertheless, two half-metallic layers electrically coupled to the superconducting film substantially affect its critical temperature and produce the spin valve effect. Within the tight-binding model for the atomically thin multilayered spin valves we show that depending on the details of the electron energy spectr…
Robustness of Spin-Triplet Pairing and Singlet-Triplet Pairing Crossover in Superconductor/Ferromagnet Hybrids
我们系统地研究了超导/铁磁结中的邻近效应，讨论了局域态密度（LDOS）的零能峰（ZEP）与自旋三重态奇频配对之间的关系。通过精确求解非线性Usadel方程，我们发现在非共线磁化的情况下，ZEP在很宽的几何参数和材料参数范围内都是可以实现的。这有力地表明了在这样的系统中由自旋三重态奇频配对诱导的ZEP的鲁棒性。我们还发现，从单重态配对到三重态配对的交叉可以通过测量F层厚度对ZEP高度的依赖性来检测。此外，我们展示了如何观察签名的自旋三重态奇频配对和配对交叉的LDOS测量。我们的研究结果提供了一个直接的方法来实验检测签名的奇频配对状态。
FeSe is argued as a superconductor in the Bardeen-Cooper-Schrieffer Bose-Einstein-condensation crossover regime where the superconducting-gap size and the superconducting transition temperature Tc are comparable to the Fermi energy. In this regime, vortex bound states should be well quantized and the preformed pairs above Tc may yield a pseudogap in the quasiparticle-excitation spectrum. We performed spectroscopic-imaging scanning tunneling microscopy to search for these features. We found Friedel-like oscillations near the vortex, which manifest the quantized levels, whereas the pseudogap was…
Destruction of superconductivity in disordered materials : a dimensional crossover
通过改变样品厚度$d$，研究了不同Nb组分$x$的非晶Nb $_{x}$ Si $_{1-x}$二维薄膜中无序诱导的超导体-绝缘体转变.我们表明，临界厚度$d_c$，从绝缘的超导制度，随着减少$x$强烈增加，从而达到超过100欧姆的值。相应的相图中的$(d, x)$平面推断和相关的三维情况。二维的超导体到绝缘体的转变与三维的超导体到金属的转变良好连接。
The Type-II/Type-I Crossover in Dirty Ferromagnetic Superconductors
本文利用脏极限扩展 Ginzburg-Landau 模型计算强无序铁磁超导体的型间区域边界，发现其与清洁情形相近，表明无序不阻碍型间超导性的实验探索。
Dimensional crossovers in the Gaussian critical fluctuations above $T_c$ of two-layer and three-layer superconductors
本文利用高斯近似下的Ginzburg-Landau泛函，计算了双层和三层超导平面系统在零外磁场下转变点以上的超导涨落能量，获得了涨落比热、磁化率和Aslamazov-Larkin顺电导的临界贡献表达式，揭示了其偏离纯2D行为的维度跨越效应。
Crossover in the local density of states of mesoscopic SNS junctions
Andreev能级耗尽了超导带隙以上的能态，这导致了介观超导体/正常金属/超导体结的局域态密度中特有的非单调交叉。这种效应在正常金属桥的长度小于相干长度的情况下尤其明显。交叉函数的显著性质是它不仅在邻近诱导间隙处消失，而且在邻近诱导间隙处也消失。在两个间隙边缘的态密度的解析表达式，以及一般结构的交叉进行了讨论。
BCS to Bose Crossover in Anisotropic Superconductors
在这项工作中，我们使用功能积分技术来研究最近邻吸引哈伯德模型上的准二维晶格。这是一个简单的唯象模型的高Tc铜氧化物，允许扩展（非本地）的s-和d-波单重态超导以及混合对称状态。该模型的Hartree-Gor'kov平均场论具有有限温度相图，该相图显示了从纯s波到纯d波超导性的转变，通过混合对称s+id状态，作为掺杂的函数。包括高斯涨落，我们研究的交叉从弱耦合BCS超导性的强耦合玻色-爱因斯坦凝聚的复合s-或d-波玻色子和评论的起源和对称性的赝隙。
Observation of Temperature-Induced Crossover to an Orbital-Selective Mott Phase in A$_{x}$Fe$_{2-y}$Se$_2$ (A=K, Rb) Superconductors
在本工作中，我们用角分辨光电子能谱研究了A $_{x}$ Fe $_{2-y}$ Se $_2$（A=K，Rb）超导体。在低温状态下，我们观察到的费米能级附近的带的轨道相关的重正化，其中的dxy带重重正化相比，dxz/dyz带。当温度升高到150 K以上时，系统演化为dxy带具有减小的光谱权重而dxz/dyz带保持金属性的状态。结合理论计算，我们的观察结果可以一致地理解为温度诱导的交叉从金属态在低温下的轨道选择性莫特相（OSMP）在高温下。此外，事实上，超导态的A $_{x}$ Fe $_{2-y}$ Se $_2$是接近这样的OSMP的边界约束系统具有足够强的现场库仑相互作用和Hund的耦合，并因此突出了非平凡的作用，在这个家庭的铁超导体中的电子相关。
Crossover between SC states in an unconventional superconductor UCoGe driven by ferromagnetic spin fluctuations
UCoGe是一种弱铁磁（FM）双带超导体（SC），其临界温度为$T_{\mathrm{SC}}\sim$ 0.7 K，居里温度为$T_{\mathrm{C}}\sim$ 3 K。我们报告奇异属性的SC和FM状态在中等磁场。观察到的现象清楚地表明，SC制度是优于顺磁状态附近的$T_{\mathrm{SC}}$。在$T_{\mathrm{SC}}$以上，零场态的特征在于具有强FM自旋波动的区域，表明接近FM量子临界点（FM-QCP）。此外，我们观察到，强大的SC制度的发展独立的存在或缺乏的长程FM订购。
3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover
我们给出了YBa_2Cu_4O_8单晶的可逆磁化数据，并分析了3D-xy临界行为和磁场诱导的3D到1D交叉的证据。观察到与这些现象的显著一致性与磁场诱导的有限尺寸效应一致，因此横向于所施加的磁场的相关长度不能增长超过极限磁长度尺度L_H。通过应用适当的标度形式，我们得到了零场临界温度，三维到一维的交叉，涡旋熔化线和有关标度变量的普适比。因此，在（H，T）平面中不存在如平均场处理所预测的沿H_c2线的连续相变。
A topological insulator (TI) interfaced with an s-wave superconductor has been predicted to host an unusual form of superconductivity known as topological superconductivity (TSC). Molecular beam epitaxy (MBE) has been the primary approach in the scalable synthesis of the TI/superconductor heterostructures. Although the growth of epitaxial TI films on s-wave superconductors has been achieved, it remains an outstanding challenge for synthesizing atomically thin TI/superconductor heterostructures, which are critical for engineering the TSC phase. Here, we used MBE to grow Bi2Se3 films with the co…
Linear nonsaturating magnetoresistance (LMR) represents a class of anomalous resistivity response to external magnetic field that has been observed in a variety of materials including but not limited to topological semi-metals, high-Tc superconductors and materials with charge/spin density wave (CDW/SDW) orders. Here we report the observation of LMR in layered kagome superconductor and CDW material CsV3Sb5 thin flakes, as well as the dimensional crossover and temperature (T) crossover of such LMR. Specifically, in ultrathin CsV3Sb5 crystals, the magnetoresistance (MR) exhibits a crossover from…
Evidence for Transition Temperature Fluctuation Induced Pinning im MgB$_2$ Superconductor
利用磁滞回线测量了MgB $_2$块材的临界电流密度$j_c(B)$随磁场的变化。不同温度下的$j_c(B)$曲线表明，当场大于交叉场$B_{sb}$时，从单涡钉扎到小束涡钉扎发生交叉。交叉场$B_{sb}(T)$的温度依赖性与随机分布的弱钉扎中心通过转变温度的空间波动（$δT_c$ -钉扎）的模型一致，而钉扎由于平均自由程波动（$δl$ -钉扎）没有观察到。
Crossover behavior for complex order parameter in high-Tc superconductors
最近的一些实验表明，在高$T_c$超导体（HTSC）的间隙对称性中存在实分量或复分量。在本文中，我们介绍了一种新的方法来研究这种复杂的序参量混合物的竞争，通过改变的位置的两体吸引势的二维扩展哈伯德哈密顿量。我们表明，这一过程解释了一些实验结果和理论方面，它可能与某些HTSC微观模型，如自旋涨落理论。按照目前的趋势，我们集中在$d_{x^2-y^2}$序参量与$d_{xy}$型或S波一样的$s_{x^2+y^2}$和$s_{xy}$对称性的组件的研究。我们发现，最佳的s-分量峰的位置与位置参数$b$的变化，而d-分量总是发生在空穴含量$ρ\approx 0.39$周围的最佳区域。
Superconductivity in strongly correlated systems is a remarkable phenomenon that attracts a huge interest. The study of this problem is relevant for materials as the high $T_c$ oxides, pnictides and heavy fermions. These systems also have in common the existence of electrons of several orbitals that coexist at a common Fermi-surface. In this paper we study the effect of pressure, chemical or applied on multi-band superconductivity. Pressure varies the atomic distances and consequently the overlap of the wave-functions in the crystal. This rearranges the electronic structure that we model inclu…
An important experimental signature of localization is the low-frequency AC conductivity, which typically vanishes as $ω^ϕ$. The exponent $ϕ= 2$ for Anderson insulators, whereas for many body localized insulators $ϕ$ is a continuously varying exponent $1 \le ϕ\le 2$. In this work, we study the low-frequency AC conductivity of localized superconductors, in which disorder is strong enough to localize all quasiparticles, while remaining weak enough to leave superconductivity intact. We find that while the ac conductivity still follows the general form $σ(ω) \sim ω^ϕ$, the exponent $ϕ$ can be mark…
Resonant and crossover phenomena in a multiband superconductor tuning the chemical potential near a band edge
在超导性质的共振，在一个政权的交叉从BCS混合玻色-费米超导，研究在一个双带超导体的化学势调谐附近的第二个迷你带的量子限制效应产生的带边。超导带隙中T=0时的形状共振（属于类Feshbach共振）表现为当化学势接近第二小带的带边时，超导能隙在第一大费米面处的干涉效应。量子阱的超晶格的情况下，被认为是在3D-2D费米表面拓扑转变的超导间隙的放大清楚地示出。结果被发现是在良好的协议与现有的实验数据上的超晶格的蜂窝状硼层插入Al和Mg间隔层。
Weak- to strong pinning crossover
硬II型超导体中的材料缺陷钉扎磁通线，从而在有限磁场的存在下建立无耗散的电流传输。根据缺陷的密度和钉扎力以及涡旋密度，钉扎是弱集体的还是强的。我们分析了无序超导体中涡旋物质的弱到强的钉扎交叉，并讨论了在这种情况下自然出现的峰值效应。
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