方钴矿相关的La $_3$ Co $_4$ Sn $_{13}$和La $_3$ Ru PDMATHAAB Sn $_{13}$化合物中无序存在下的超导电性：电输运和磁研究
Superconductivity in the presence of disorder in skutterudite-related La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ compounds; electrical transport and magnetic studies
A. Slebarski, M. M. Maska, M. Fijalkowski, C. A. McElroy, M. B. Maple
La $_3$ Co $_4$ Sn $_{13}$和La $_3$ Ru $_4$ Sn $_{13}$被归类为BCS超导体。在临界场$H_{c2}$对$T$的曲线图中，La $_3$ Ru $_4$ Sn $_{13}$在较高的临界温度$T_c^{\star}$下显示第二超导相，这是非均匀超导体的特征，而La $_3$ Co $_4$ Sn $_{13}$在低于$T_c$下显示体超导性。我们观察到的临界温度与外部压力和磁场的降低与$\frac{dT_c^{\star}}{dP} > \frac{dT_c}{dP}$的两种化合物。根据McMillan理论解释了$T_c$的压力依赖性，并将其理解为晶格硬化的结果。对La-$_3$-Co-$_x$-Ru-$_{4-x}$-Sn-$_{13}$超导态的研究表明，对于$x<4$，$T_c^{\star}$大于$T_c$.这种独特的和意想不到的观察结果进行了讨论，作为一个结果的局部无序和/或化学压力的影响时，Ru原子被部分取代较小的Co原子。
英文摘要：
La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ were categorized as BCS superconductors. In a plot of the critical field $H_{c2}$ vs $T$, La$_3$Ru$_4$Sn$_{13}$ displays a second superconducting phase at the higher critical temperature $T_c^{\star}$, characteristic of inhomogeneous superconductors, while La$_3$Co$_4$Sn$_{13}$ shows bulk superconductivity below $T_c$. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds with $\frac{dT_c^{\star}}{dP} > \frac{dT_c}{dP}$. The pressure dependences of $T_c$ are interpreted according to the McMillan theory and understood to be a consequence of lattice stiffening. The investigation of the superconducting state of La$_3$Co$_x$Ru$_{4-x}$Sn$_{13}$ shows a $T_c^{\star}$ that is larger then $T_c$ for $x<4$. This unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.
We report superconductive iridium pnictides BaxIr4X12 (X = As and P) with a filled skutterudite structure, demonstrating that Ba filling dramatically alters their electronic properties and induces a nonmetal-to-metal transition with increasing the Ba content x. The highest superconducting transition temperatures are 4.8 and 5.6 K observed for BaxIr4As12 and BaxIr4P12, respectively. The superconductivity in BaxIr4X12 can classified into the Bardeen-Cooper-Schrieffer type with intermediate coupling.
The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide superconductors whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers in a unit cell. When n=3 (the 10-3-8 phase), the undoped compound is an antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the undoped compound is a superconductor with the transition temperature of 26K. Here we report the results of high-pressure studies on the 10-3-8 compound obtained through a combination of in-situ resistance, magnetic susceptibility, and Hall coefficient measurements. We find that its AFM order …
We report an investigation of the superconducting states of $\mathrm{Lu}_3\mathrm{Os}_4\mathrm{Ge}_{13}$ and $\mathrm{Y}_3\mathrm{Ru}_4\mathrm{Ge}_{13}$ single crystals by measurements of the electrical resistivity, ac susceptibility and London penetration depth. The analysis of the penetration depth and the derived superfluid density indicates the presence of nodeless superconductivity and suggest that there are multiple superconducting gaps in both materials. Furthermore, ac susceptibility measurements of both compounds display the peak effect in the low temperature region of the $H-T$ phase…
We report a study of the superconducting and normal-state properties of the filled-skutterudite system PrPt$_{4}$Ge$_{12-x}$Sb$_x$. Polycrystalline samples with Sb concentrations up to $x =$ 5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to $x =$ 4, above which, no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, $γ$, of superconducting specimens decreases with increasing $x$…
The interplay between superconductivity and structural phase transition has attracted enormous interests in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ir$_{4}$Sn$_{13}$ ($x$ = 0, 0.5, 1) and Ca$_{3}$Rh$_{4}$Sn$_{13}$ show some unusual properties similar to the Fe-pnictides, through $^{119}$Sn nuclear m…
Here we report on a new kind of compound, XδIr4X12-δ (X = P, As), the first hole-doped skutterudites superconductor. We provide atomic resolution images of the caging As atoms using scanning transmission electron microscopy (STEM). By inserting As atoms into the caged structure under a high pressure, superconductivity emerges with a maximum transition temperature (Tc) of 4.4 K (4.8 K) in IrAs3 (IrP3). In contrast to all of the electron-doped skutterudites, the electronic states around the Fermi level in XδIr4X12-δ are dominated by the caged X atom, which can be described by a simple body-cente…
Evidence for s-wave superconductivity with antiferromagnetic fluctuations in filled skutterudite LaFe$_{4}$P$_{12}$: $^{139}$La and $^{31}$P-NMR studies
我们对填充方钴矿超导体LaFe $_{4}$ P $_{12}$进行了$^{139}$ La，$^{31}$ P-NMR研究，其临界温度为$T_c=4.1$ K。在正常状态下，反铁磁（AFM）波动的存在下，有限波矢建议从核自旋晶格弛豫率$1/T_1$和奈特位移之间的关系。在超导（SC）状态下，观察到明显的相干峰$T_c$下方，很容易被抑制的外加电场。观察到$1/T_1$的指数下降，暗示了具有$2Δ/k_{\rm B}T_c =3.8$的各向同性超导带隙。此外，我们观察到骑士位移的减少，表明$T_c$以下的单对形成。这些结果清楚地证明了LaFe $_{4}$ P $_{12}$是一种罕见的具有显著AFM涨落的s波超导体。
We investigated the superconducting order parameter of the filled skutterudite LaPt4Ge12, with a transition temperature of Tc = 8.3 K. To this end, we performed temperature and magnetic-field dependent specific-heat and thermal-conductivity measurements. All data are compatible with a single superconducting s-wave gap. However, a multiband scenario cannot be ruled out. The results are discussed in the context of previous studies on the substitution series Pr1-xLaxPt4Ge12. They suggest compatible order parameters for the two end compounds LaPt4Ge12 and PrPt4Ge12. This is not consistent with a s…
Muon spin rotation ($μ$SR) and inelastic X-ray scattering (IXS) were used to investigate the superconducting properties of the filled-skutterudite compound LaRu$_{4}$As$_{12}$. A two-gap isotropic ($s+s$)-wave model can explain the temperature dependence of the superfluid density. Zero field $μ$SR measurements confirm that the time-reversal symmetry does not break upon entering the superconducting state. The measurements of lattice dynamics at 2, 20 and 300 K revealed temperature dependencies of the phonon modes that do not follow strictly a hardening of phonon frequencies upon cooling as expe…
Weak Interband-Coupling Superconductivity in the Filled Skutterudite LaPt4Ge12
利用隧道二极管振荡器（TDO）方法测量了LaPt $_{4}$ Ge $_{12}$的磁穿透深度$λ(T,B)$和超流密度$ρ_s(T)$，并利用横场μ子自旋旋转（$μ$ SR）谱研究了超导体的超导配对态.在$T\ll T_{c}$处，$λ(T)$遵循指数型温度依赖关系，但其零温度值$λ(0)$随磁场线性增加。详细的分析表明，$λ(T)$和相应的$ρ_{s}(T)$，测量的迈斯纳态的TDO方法是很好地描述了一个双间隙$γ$模型与间隙大小的$Δ_1(0)=1.31k_{B}T_c$和$Δ_2(0)=1.80k_{B}T_c$和一个非常弱的带间耦合。相比之下，$ρ_s(T)$，从$μ\rm{SR}$的数据在一个小的领域，可以通过一个单一的间隙BCS模型与接近$Δ_2(0)$的间隙。我们得出结论：LaPt $_{4}$ Ge $_{12}$是一种边缘双能隙超导体，小能隙$Δ_1$似乎被小磁场破坏。相比之下，在PrPt $_4$ Ge $_{12}$中，$4f$ -电子可以增强带间耦合，因此，产生更稳健的多带超导性。
Evidence for Point Nodes in the Superconducting Gap Function in the Filled Skutterudite Heavy-Fermion Compound PrOs4Sb12: 123Sb-NQR Study under Pressure
Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe$_4$As$_{12}$ [Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out $^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in a newly discovered isostructural superconductor SrOs$_4$As$_{12}$ with a superconducting transition temperature of $T_{\rm c}$ $\sim$ 4.8 K. Knight shift $K$ determined by the NQR spectrum under a small magnetic field ($\le$ 0.5 T) is nearly independent of temperature, …
Superconductivity of La$_3$Co$_4$Sn$_{13}$ and La$_3$Rh$_4$Sn$_{13}$: A comparative study
本文报道了方钴矿相关的LaPDMATHABMM Co $_4$ Sn $_{13}$和LaPDMATHABMM Rh $_4$ Sn $_{13}$超导体的电输运和热力学性质。对LaPDMATHABMM-Rh-$_4$-Sn $_{13}$施加外压，电阻超导临界温度Tc降低，而LaPDMATHABMM-Co-$_4$-Sn $_{13}$的临界温度随外压的增加而提高。正压力系数dTc/dP与La $_3$ Co $_4$ Sn $_{13}$中的微妙结构转变相关，并在晶格不稳定性的背景下进行了讨论。比热数据表明这两种化合物都是典型的BCS超导体。然而，La $_3$ Rh $_4$ Sn $_{13}$在较高温度下也表现出第二超导相，这是非均匀超导体的特征。计算了非均匀超导相的比热，与LaPDMATHABMM Rh $_4$ Sn $_{13}$的C（T）实验数据符合得很好.我们还发现，施加的压力减少了第二超导相。
Higher-Order Topological Superconductivity and Electrically Tunable Majorana Corner Modes in Monolayer MnXPb$_2$ (X=Se, Te)-Pb Heterostructure
Institute of Applied Physics and Computational Mathematics（应用物理与计算数学研究所）；Anhui Provincial Key Laboratory of Low-Energy Quantum Materials and Devices, High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences（中国科学院合肥物质科学研究院强磁场科学中心安徽低能量子材料与器件重点实验室）；Science Island Branch of Graduate School, University of Science and Technology of China（中国科学技术大学研究生院合肥科学岛分院）；National Key Laboratory of Computational Physics（计算物理学国家重点实验室）；School of Physics and Physical Engineering, Qufu Normal University（曲阜师范大学物理工程学院）
We report a detailed study of superconductivity in polycrystalline SnTaS$_2$ using electrical transport, magnetization and heat capacity measurements. SnTaS$_2$ crystallizes in centrosymmetric hexagonal structure with space group $P6_3/mmc$. Electrical resistivity, magnetization and specific heat data suggest SnTaS$_2$ to be a weakly coupled, type-II superconductor with $T_c \approx$ 2.8 K. First-principles calculations show signature for nodal line topology in the electronic band structure, protected by the spatial-inversion and time-reversal symmetries, that strongly gapped out by the inclus…
Charge density waves and superconductivity in the electron-positive fermion gas using a simple intuitive model. Part II: Collective modes, effective interactions, superconductivity, and transport
Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (Ca$_x$Sr$_{1-x}$)$_3$Rh$_4$Sn$_{13}$
超导准方钴矿（Ca $_x$ Sr $_{1-x}$）$_3$ Rh $_4$ Sn $_{13}$族的结构量子临界点为$x_c=0.9$，超导转变温度$T_c$在该临界点附近有一个圆顶形的变化，我们用比热探测了整个系列跨越量子临界点的正常态和超导态.我们的分析表明，一个显着降低的有效德拜温度接近$x_c$，我们解释为伴随着结构不稳定性的声子软化的结果。此外，在结构量子临界点附近发现$2Δ/k_BT_c$和$ΔC/γT_c$的显著大的增强超过Bardeen-Cooper-Schrieffer（BCS）值。（Ca $_{x}$ Sr $_{1-x}$）$_3$ Rh $_4$ Sn $_{13}$的相图为研究结构量子临界性和强电子-声子耦合超导电性之间的相互作用提供了一个模型系统。
Electrons confined to two dimensions display an unexpected diversity of behaviors as they are cooled to absolute zero. Noninteracting electrons are predicted to eventually "localize" into an insulating ground state, and it has long been supposed that electron correlations stabilize only one other phase: superconductivity. However, many two-dimensional (2D) superconducting materials have shown surprising evidence for metallic behavior, where the electrical resistivity saturates in the zero-temperature limit, the nature of this unexpected metallic state remains under intense scrutiny. We report …
Evolution of crystalline electric field effects, superconductivity, and heavy fermion behavior in the specific heat of Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$
Twisted graphene multilayers have demonstrated to yield a versatile playground to engineer controllable electronic states. Here, by combining first-principles calculations and low-energy models, we demonstrate that twisted graphene trilayers provide a tunable system where van Hove singularities can be controlled electrically. In particular, it is shown that besides the band flattening, bulk valley currents appear, which can be quenched by local chemical dopants. We finally show that in the presence of electronic interactions, a non-uniform superfluid density emerges, whose non-uniformity gives…
We investigate the physical mechanisms for achieving an electrical control of conventional spin-singlet superconductivity in thin films by focusing on the role of surface orbital polarization. Assuming a multi-orbital description of the metallic state, due to screening effects the electric field acts by modifying the strength of the surface potential and, in turn, yields non-trivial orbital-Rashba couplings. The resulting orbital polarization at the surface and in its close proximity is shown to have a dramatic impact on superconductivity. We demonstrate that, by varying the strength of the el…
Since the discovery of superconductivity at 200 K in H3S [1] similar or higher transition temperatures, Tcs, have been reported for various hydrogen-rich compounds under ultra-high pressures [2]. Superconductivity was experimentally proved by different methods, including electrical resistance, magnetic susceptibility, optical infrared, and nuclear resonant scattering measurements. The crystal structures of superconducting phases were determined by X-ray diffraction. Numerous electrical transport measurements demonstrate the typical behaviour of a conventional phonon-mediated superconductor: ze…
