The temperature dependence of electron spin resonance (ESR) was studied in $EuFe_{2-x}Co_{x}As_2 $ (x = 0.0, 0.067, 0.1, 0.2, 0.25, 0.285, 0.35, 0.4 and 0.5). The ESR spectrum of all the samples indicates that the g factor and peak-to-peak linewidth strongly depend on the temperature. Moreover, the peak-to-peak linewidth shows the Korringa behavior, indicating an exchange coupling between the conduction electrons and the $Eu^{2+}$ions. The linewidth, g factor and the integrate ESR intensity show anomalies at the temperature of the spin-density-wave (SDW). The linewidth below the SDW transition does not rely on the temperature. This gives the evidence of the gap opening at the $T_{SDW}$. The slope of the linewidth is closely associated to $T_{SDW}$and $T_C$. This exotic behavior may be related to the nesting of the Fermi surface.
Signatures of quantum criticality in hole-doped and chemically pressurized EuFe_2As_2 single crystals
通过测量热电势$S(T)$和电阻率$ρ(T)$，研究了$_x$ Eu $_{1-x}$ Fe $_2$ As $_2$和EuFe $_2$（As $_{1-y}$ P $_y$）$_2$单晶中空穴掺杂和化学压力（等价掺杂）的效应.掺杂后$S(T)$的演变表明，在临界值$x_{\mathrm{cr}}=0.3$和$y_{\mathrm{cr}}=0.21$，分别电子配置的急剧变化，自旋密度波跃迁被完全抑制和超导性（SC）出现。对于化学压力的情况下，与已发表的ARPES测量结果的比较表明，在$y_{cr}$的Lifshitz转变。温度依赖性$S(T)/T\propto \log T$和$Δρ\propto T$观察到的正常状态以上的SC过渡建议在这两个系统中的量子临界。
By performing high-pressure single-crystal neutron diffraction measurements, the evolution of structure and magnetic ordering in EuFe2As2 under hydrostatic pressure were investigated. Both the tetragonal-toorthorhombic structural transition and the Fe spin-density-wave (SDW) transition are gradually suppressed and become decoupled with increasing pressure. The antiferromagnetic order of the Eu sublattice is, however, robust against the applied pressure up to 24.7 kbar, without showing any change of the ordering temperature. Under the pressure of 24.7 kbar, the lattice parameters of EuFe2As2 di…
Study of the anisotropic magnetic order of the Eu sublattice in single crystals of EuFe_2-xCo_xAs_2 (x = 0, 0.2) by means of magnetization and magnetic torque
In this work, we report ferromagnetic resonance spectroscopy of EuFe2As2 single crystals. We observe ferromagnetic resonance responses, which are attributed to antiferromagnetic resonances of Eu sub-lattice with orthorhombic crystal structure and with different orientations of twin domains relative to the external field. We confirm validity of the recently-proposed spin Hamiltonian with anisotropic Eu-Eu exchange interaction and biquadratic Eu-Fe exchange interaction.
In this work, fabrication and characterization of magnetic properties of EuFe2As2 and EuRbFe4As4 single crystals is reported. Magnetization measurements of samples with well defined thin film geometry and crystal orientation demonstrate a striking similarity in ferromagnetic properties of Eu subsystems in these two compounds. Measurements with magnetic field applied along ab crystal planes reveal meta-magnetic transition in both compounds. Numerical studies employing the Jz1-Jz2 Heisenberg model suggest that the ground state of the magnetic order in Eu subsystem for both compounds is the helic…
Interplay of magnetism and superconductivity in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals probed by muon spin rotation and ${}^{57}$Fe Mössbauer spectroscopy
Varying Eu$^{2+}$ magnetic order in EuFe$_2$As$_2$ by chemical pressure
在铁122磷属元素化物超导体中，EuFe $_2$ As $_2$系列引起了特别的兴趣，因为除了Fe子系统中的超导性或长程自旋密度波序之外，低温下的局域化Eu $^{2+}$磁矩序。在这里，我们提出了一个新的计划，如何在铕化合物的自旋排列时，压力变化的耦合，我们解释EuFe $_2$（作为$_{1-x}$ P $_x$）$_2$单晶的磁化测量以及其他观察的Eu $^{2+}$订购以前在文献中报道。甚至在母体化合物EuFe $_2$ As $_2$中，Eu $^{2+}$离子的磁矩也略微倾斜，产生沿$c$ -方向的铁磁贡献，该铁磁贡献随着压力而变强。进一步减小层间距离，$ab$平面的反铁磁耦合最终变成铁磁。
The EuFe(2-x)Ni(x)As2 compounds exhibiting 3d and/or 4f magnetic order were investigated by means of 57Fe and 151Eu Mössbauer spectroscopy. Additionally, results for the end members of this system, i.e. EuFe2As2 and EuNi2As2, are reported for comparison. It was found that spin-density-wave order of the Fe itinerant moments is monotonically suppressed by Ni-substitution. However, the 3d magnetic order survives at the lowest temperature up to at least x = 0.12 and it is certainly completely suppressed for x = 0.20. The Eu localized moments order regardless of the Ni concentration, but undergo a …
本文用Eu-$^{2+}$电子自旋共振（ESR）方法研究了EuFe-$_{2-x}$-Co-$_x$-As-$_2$-$(0 \leq x \leq 0.4)$和EuFe-$_2$-As-$_{2-y}$-P-$(0 \leq y \leq 0.43)$-$(0 \leq y \leq 0.43)$的单晶相图。从交换窄化ESR谱线的线宽$ΔH(T)$的温度依赖性中，可以清楚地区分自旋密度波（SDW）$(T < T_{\rm SDW})$和正常金属区$(T > T_{\rm SDW})$。在$T > T_{\rm SDW}$的线宽的各向同性线性增加是由柯林加弛豫驱动的，柯林加弛豫测量费米能级处的导电电子态密度。对于$T < T_{\rm SDW}$，各向异性探测局部配体场，而与传导电子的耦合消失。随着取代$x$或$y$的增加，转变温度$T_{\rm SDW}$线性降低，伴随着Korringa弛豫速率从$x=y=0$的8 Oe/K线性降低到$x \approx 0.2$或$y \approx 0.3$的超导性开始时的3 Oe/K，在此之上它几乎保持恒定。对Eu稀释的SDW化合物Eu $_{0.2}$ Sr $_{0.8}$ Fe $_2$ As $_2$和超导（SC）Eu $_{0.22}$ Sr $_{0.78}$ Fe $_{1.72}$ Co $_{0.28}$ As $_2$单…
The interplay of magnetism and superconductivity (SC) has been a focus of interest in condensed matter physics for decades. EuFe2As2 has been identified as a potential platform to investigate interactions between structural, magnetic, electronic effects as well as coexistence of magnetism and SC with similar transition temperatures. However, there are obvious inconsistencies in the reported phase diagrams of Eu(Fe1-xCox)2As2 crystals grown by different methods. For transition metal arsenide (TMA)-flux-grown crystals, even the existence of SC is open for dispute. Here we re-examine the phase di…
This study investigates the changes of magnetic ordering temperature via nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to such local lattice variations. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Neel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a 122 pa…
Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsO$_{x}$F$_{1-x}$ single crystals
本文报道了氧铌酸铁超导体NdFeAsO $_{1-x}$ F $x$单晶的平面偏振喇曼散射光谱。该光谱表现出尖锐和对称的声子线与氟掺杂$x$弱的依赖性。温度依赖性没有显示任何声子异常的超导转变。铁相关的声子强度显示出强烈的共振增强低于2eV。我们将共振增强与在光学电导率中观察到的约2 eV的带间跃迁的存在相关联。我们的研究结果指出，在铁氧铌酸盐超导体的拉曼活性声子和电子激发之间的一个相当弱的耦合。
Magnetic and superconducting properties on S-type single-crystal CeCu$_2$Si$_2$ probed by $^{63}$Cu nuclear magnetic resonance and nuclear quadrupole resonance
我们进行了$^{63}$ Cu核磁共振/核四极共振测量，以研究CeCu $_2$ Si $_2$的“超导主导”（$S$型）单晶的磁性和超导（SC）性质。虽然反铁磁（AFM）涨落的发展下降到1~K表明AFM临界性接近，但在0.8~K以下观察到Korringa行为，而在$T_{\rm c} \sim$ 0.6 K以上没有观察到磁异常。这些行为在$S$型CeCu $_2$ Si $_2$中是预期的。零场下的核自旋-晶格弛豫速率$1/T_1$的温度依赖性在130 mK以下与以前的多晶样品几乎相同，但在120 mK以下则向下偏离。事实上，SC态的$1/T_1$可以用双能隙$s_{\pm}$ -波模型来拟合，而不是用双能隙$s_{++}$ -波模型来拟合。在磁场下，在两个方向上的自旋磁化率明显降低到低于$T_{\rm c}$，表明形成了自旋单重态配对。自旋磁化率的剩余部分由$1/T_1T$计算的场致剩余态密度来理解，这归因于涡核的影响。在上临界场$H_{c2}$以上没有观察到磁异常，但观察到AFM涨落的发展，表明在强AFM涨落中实现了超导。
Raman resonance in iron-based superconductors: The magnetic scenario
我们对NaFe $_{1-x}$ Co $_x$ As、EuFe $2$ As $_2$、SrFe $_2$ As $_2$和Ba（Fe $_{1-x}$ Co $_x$）$_2$作为$_2$，关注在$B_{1g}$对称通道中看到的两个特征（在一个Fe晶胞符号中）：在正常状态下的静态，均匀的拉曼响应的强烈的温度依赖性和在超导状态下的集体模式的存在。我们表明，这两个功能可以解释的耦合费米子对磁波动通过Aslamazov-Larkin过程。我们首先分析了磁介导的拉曼强度在领先的两个回路的顺序，然后包括对磁波动之间的相互作用。我们发现，在$B_{1g}$通道中的全拉曼强度可以被看作是光通过Aslamazov-Larkin过程耦合到Ising-Err磁化率的结果。我们认为，在正常状态下的奇异温度依赖性的组合的Aslamazov-Larkin顶点的温度依赖性和伊辛-伊辛磁化率。我们讨论两种情况下的共振低于$T_c$。在一个，共振是由于在完全重整化伊辛-爱因斯坦磁化率的极点的发展。另一种是轨道激子的情形，在这种情形中，自旋涨落在低能费米子之间产生吸引力的相互作用。
We study the out-of-equilibrium dynamics of a Bardeen-Cooper-Schrieffer condensate subject to a periodic drive. We demonstrate that the combined effect of drive and interactions results in emerging parametric resonances, analogous to a vertically driving pendulum. In particular, Arnold tongues appear when the driving frequency matches $2Δ_0/n$, with $n$ a natural number, and $Δ_0$ the equilibrium gap parameter. Inside the Arnold tongues we find a commensurate time-crystal condensate which retains the $U(1)$ symmetry breaking of the parent superfluid/superconducting phase and shows an additiona…
In this work, we report the broad-band ferromagnetic resonance spectroscopy of EuSn$_2$As$_2$ single crystals at different temperatures in combination with magnetization measurements and structural characterization. We observe conventional collective acoustic resonance mode of the A-type antiferromagnetic spin-flop phase in the Eu sub-lattice, and its transition to the paramagnetic resonance above the ordering temperature. Furthermore, we observe reproducibly additional well-defined spectral line. The origin of the additional line remains unclear. However, its temperature dependence attributes…
