The filled skutterudite superconductor PrPt4Ge12 was studied in muon-spin rotation (muSR), specific heat, and electrical resistivity experiments. The continuous increase of the superfluid density with decreasing temperature and the dependence of the magnetic penetration depth λon the magnetic field obtained by means of muSR, as well as the observation of a T^3 dependence of the electronic specific heat establish the presence of point-like nodes in the superconducting energy gap. The energy gap was found to be well described by Δ=Δ_0| k_x - ik_y| or Δ= Δ_0(1 - k_y^4) functional forms, similar to that obtained for another skutterudite superconductor, PrOs4Sb12. The gap to T_c ratios were estimated to be Δ_0/k_BT_c = 2.68(5) and 2.29(5), respectively.
The claim in Barkman et al [Physical Review Letters {\bf 122}, 165302 (2019)] that pair-density wave (PDW) superconductivity in magnetic field is more stable near surface than in bulk, is not supported by microscopic theory.
Fulde, Ferrell, Larkin, and Ovchinnikov (FFLO) predicted inhomogeneous superconducting and superfluid ground states, spontaneously breaking translation symmetries. In this Letter, we demonstrate that the transition from the FFLO to the normal state as a function of temperature or increased Fermi surface splitting is not a direct one. Instead the system has an additional phase transition to a different state where pair-density-wave superconductivity (or superfluidity) exists only on the boundaries of the system, while the bulk of the system is normal. The surface pair-density-wave state is very…
The recent Comment by Vorontsov [arXiv:2007.13696] claims that surface pair-density-wave superconductivity with critical temperature higher than the bulk FFLO critical temperature is not supported by microscopic theory. The conclusion is reached by using an approximate semi-microscopic quasiclassical approach. Here we show that a fully microscopic approach unambiguously demonstrates the existence of surface pair-density-wave superconductivity.
Evolution of the Superfluid Density in Infinite-Layer Nickelates
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory（斯坦福材料能源科学研究所，SLAC国家加速器实验室）；Department of Physics, Stanford University（斯坦福大学物理系）；Department of Applied Physics, Stanford University（斯坦福大学应用物理系）；Department of Physics and Astronomy, University of Rochester（罗切斯特大学物理与天文学系）
Effect of thermal phase fluctuations on the superfluid density of two-dimensional superconducting films
在0.4 K ~ Tc范围内对Mo_（77）Ge_（23）薄膜的复薄层电导率进行了高精度测量。在低于平均场转变温度Tco的温度Tc处，观察到逆薄层电感1/L（T）的急剧下降。就在Tc以下，1/L（T）被抑制到其平均场值以下，表明纵向相位起伏几乎具有其全部经典振幅，但它们随着T的减小而迅速消失。我们认为，有一个量子交叉在约0.94 Tco，低于经典的相位波动被抑制。
Local measurement of the superfluid density in the pnictide superconductor Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ across the superconducting dome
我们使用局部技术测量Ba（Fe $_{1-x}$ Co $_{x}$）$_2$ As $_2$中的渗透深度$λ_{ab}(T)$，该技术不对样品求平均值。超流密度$ρ_s(T)\equiv1/λ_{ab}(T)^2$具有三个主要特征。首先，$ρ_s(T=0)$在圆顶的欠掺杂侧急剧下降。第二，$λ_{ab}(T)$在最佳掺杂下在低$T$下是平坦的，表明完全带隙的超导性，但在欠掺杂和过掺杂样品中变化更强烈，与幂律或小的第二间隙一致。第三，$ρ_s(T)$在$T_c$附近急剧变化以获得最佳掺杂和欠掺杂。这些观察结果与磁相和超导相之间的相互作用是一致的。
Superfluid helium's low-loss dielectric properties, excellent thermal conductivity, and unique collective excitations make it an attractive candidate to incorporate into superconducting qubit systems. We controllably immerse a three-dimensional superconducting transmon qubit in superfluid helium-4 and measure the spectroscopic and coherence properties of the system. We find that the cavity, the qubit, and their coupling are all modified by the superfluid, which we analyze within the framework of circuit quantum electrodynamics (cQED). At at temperatures relevant to quantum computing experiment…
We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for highly unconventional superconducting states with the coexistence of chiral d-wave superconductivity, charge density waves and pair density waves in the strained graphene. Our results show that the strain-induced flat bands can promote the superconducting transition temperature approximately $50\%$ compared to that of the original doped graphene, which suggests that the flat-band superconductivity is a potential route to get superconductivity with higher critical temperatures. In particular, we…
Vortex Fluctuations in the Critical Casimir Effect of Superfluid and Superconducting Films
用涡环重整化方法计算了超流膜中临界Casimir力的大小。当热涡环的大小与薄膜厚度相当时，力变得明显，并且T Tc的结果< Tc are found to match very well with perturbative renormalization theories that have only been carried out for T >。当施加到连接到大块样品的高Tc超导膜时，卡西米尔力导致膜和大块之间出现电压差，估计表明这可能是容易测量的。
Magnetic penetration-depth measurements of a suppressed superfluid density of superconducting Ca$_{0.5}$Na$_{0.5}$Fe$_2$As$_2$ single crystals by proton irradiation
本文报道了质子辐照产生的随机点缺陷对超导Ca $_{0.5}$ Na $_{0.5}$ Fe $_2$ As $_2$单晶超流密度$ρ_{s}$的显著影响。抑制的大小是通过使用磁力显微镜测量与温度相关的磁穿透深度$λ(T)$来推断的。我们的研究结果表明，辐射剂量为2 $\times10^{16}$ cm $^{-2}$由3 MeV的质子产生的超导临界温度$T_{c}$的减少约10%的结果。%，而上临界场的斜率没有明显的变化。相反，$ρ_{s}(0)$被抑制约60%。Abrikosov-Gorkov理论的这种崩溃可以用所谓的“瑞士奶酪模型”来解释，该模型解释了类似于瑞士奶酪中的孔的点缺陷附近的序参数的空间抑制。上临界场的斜率和穿透深度$λ(T/T_{c})/λ(0)$在辐照前后表现出相似的温度依赖性。这可能是由于Ca $_{0.5}$ Na $_{0.5}$ Fe $_2$ As $_2$的高度无序性质与大的带内和同时带间散射以及短相干长度超导性的$s^\pm$波性质的组合。
High-$T_c$ Berezinskii-Kosterlitz-Thouless transition in 2D superconducting systems with coupled deep and quasi-flat electronic bands with van Hove singularities
Scaling of the superconducting transition temperature in underdoped high-Tc cuprates with a pseudogap energy: Does this support the anyon model of their superfluidity?
In the seminal work by G. Eilenberger [Z. Phys. 214, 195 (1968)], the quasiclassical expression for the free energy of spin-singlet superconductor has been suggested. Starting from the Luttinger-Ward formulation we derive the Eilenberger free energy and find its generalization for superconductor or superfluid with spin-triplet correlations. Besides ordinary superconductors with various scattering mechanisms, the obtained free energy functional can be used for systems with spin-triplet pairing such as superfluid $^3$He and superconducting systems with spatially-inhomogeneous exchange field or s…
Nambu identity and collective modes in superconductors and superfluid $^3$He
集体模式在从超导体到超流体$^{3}$ He的各种不同的物理系统中表现出来。集体模是通过基于对称性破缺双阱势的Higgs-Anderson机制产生的。最近，在超导NbN和InO中，在强太赫兹激光场的存在下，集体模式进行了探索。在这两种情况下，发现了一个单一的集体模式，其振荡频率是超导能隙$Δ$的两倍。超流体$^{3}$他是各种集体模式的宿主。特别是，在超流$^{3}$ He B相，两个大规模的集体模式被发现与质量$\sqrt{{8}/{5}}Δ$和$\sqrt{{12}/{5}}Δ$。我们表明，对于这两种情况下的超导薄膜和超流$^{3}$他B相，集体模式满足南布身份，涉及到不同的集体模式的质量的能隙参数$Δ$。
A sufficiently large parallel magnetic field will generate staggered supercurrent loops and superfluid density wave in two weakly linked superconducting (SC) ultrathin films, resulting in an inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The SC order parameter of such an FFLO state is characterized by Bloch wave functions, called the "Bloch SC state". The staggered supercurrent loops form an array of Josephson vortex-antivortex pairs, instead of the usual Josephson vortex lattice. Enclosing a unit cell of the array, the London's fluxoid is quantized as $Φ^{\prime}=Φ_0=hc/2e$, whi…
We consider a clean layered magnetic superconductor in which a continuous magnetic transition takes place inside superconducting state and the exchange interaction between superconducting and magnetic subsystems is weak so that superconductivity is not destroyed at the magnetic transition. An example of such material is RbEuFe$_{4}$As$_{4}$. We investigate the suppression of the superconducting gap and superfluid density by correlated magnetic fluctuations in the vicinity of the magnetic transition. The influence of nonuniform exchange field on superconducting parameters is sensitive to the re…
