砷化铁的正常态表现出弱的金属行为，并伴有强烈的磁涨落。特别是，一些FeAs-1111和FeAs-122化合物在低温下表现出自旋密度波（SDW）转变和电阻率对数上升的线性T依赖性。我们认为这是由于近藤效应与SDW共存的未掺杂FeAs层中载流子与局域磁矩之间的自旋翻转散射造成的。这种情况也占的变化的磁阻从正到负的Sr 3Sc 2 O 5 Fe 2As 2化合物。
英文摘要：
The normal state of the iron arsenides shows the poor metallic behavior mixed with strong magnetic fluctuations. In particular, some FeAs-1111 and FeAs-122 compounds show the linear-T dependence of susceptibility above the spin-density wave (SDW) transition and the logarithmic upturn of resistivity at low temperatures. We suggest that this is due to the spin-flip scattering between the charge carriers and the local moments in the undoped FeAs layer where Kondo effect coexists with the SDW. This scenario is also accounted for the change of the magnetoresistance from positive to negative in the Sr3Sc2O5Fe2As2 compound.
Unconventional pairing in the iron arsenide superconductors
我们用磁长程序作为工具来探测砷化铁超导体中的库珀对波函数。我们从理论上证明，只有当库珀对形成一个非常规的，符号变化的状态，反铁磁性和超导性可以共存于这些材料。在Ba（Fe $_{1-x}$ Co $_{x}$）$_{2}$ As $_{2}$中共存的观察则证明了该材料中的非常规配对。理论和中子衍射实验之间的详细协议，特别是不寻常的行为的磁序低于$T_{c}$，证明了我们的结论的鲁棒性。我们的研究结果强烈地表明，在砷化铁家族的所有成员中，超导性都是非常规的。
We report anomalous critical transport behavior in a GaAs structure containing a dense array of ErAs quantum dots. The structure displays a voltage (electric field)-controlled insulator-to-metal transition and strong hysteresis in the Kondo-like current-vs-temperature characteristic, with critical temperatures as high as 50 K. We attribute this behavior to a strong distributed Kondo resonance between the quantum dots after the Coulomb blockade of the array is lifted. This is consistent with a high sensitivity of the phase transition to a small external magnetic field that we have observed in t…
Measurement of the elastoresistivity coefficients of the underdoped iron-arsenide Ba(Fe$_{0.975}$Co$_{0.025}$)$_2$As$_2$
本文提出了一种测量具有四重对称性的单晶样品的弹性电阻率张量$m_{ij}$中各项的新方法。该技术被施加到一个代表性的欠掺杂的铁砷化物，Ba（Fe $_{0.975}$ Co $_{0.025}$）$_2$ As $_2$，揭示了一个巨大的和各向异性的弹性电阻相比，简单的金属。的$m_{66}$系数如下居里-外斯温度依赖性，提供直接的证据表明，在$T_s$ = 97.5 K时发生在该材料中的四方到正交结构相变是不是一个真正的适当的铁弹性转变的结果。相反，该材料遭受伪适当的转变，其中晶格应变不是主要的序参量。
In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types of magnetic orders disappear abruptly and a narrow SC dome develops. With further increasing pressure characteristics of a Kondo-lattice system become more and more apparent in the electrical resistivity. This su…
The thermal conductivity k of the iron-arsenide superconductor K-Ba122 was measured down to 50 mK in a magnetic field up to 15 T, for a heat current parallel and perpendicular to the tetragonal c axis. In the range from optimal doping (x ~ 0.4) down to x = 0.16, there is no residual linear term in k(T) at T = 0, showing that there are no nodes in the superconducting gap anywhere on the Fermi surface. Upon crossing below x = 0.16, a large residual linear term suddenly appears, signaling the onset of nodes in the superconducting gap, most likely vertical line nodes running along the c axis. We d…
Electronic Nematicity Revealed by Torque Magnetometry in Iron Arsenide EuFe$_2$(As$_{1-x}$P$_x$)$_2$
电子向列相是一种电子取向的有序性，它打破了铁磷属元素化物超导体的旋转对称性。然而，这一阶段的掺杂依赖性的普遍性和它的关系，其他的破缺订单（如超导）在不同的家庭的铁pnictides，仍然是悬而未决的问题。本文用转矩磁法研究了EuFe $_2$（As $_{1-x}$ P $_x$）$_2$在不引入外压的情况下的转动对称破缺。发现在最佳掺杂下，超导相在结构转变上方增殖并持续进入超导状态，之后它变得不存在或非常弱，与BaFe $_2$（As $_{1-x}$ P $_x$）$_2$中观察到的行为形成鲜明对比。这些测量结果表明，在超导圆顶下，接近最佳掺杂的假定量子跃迁。
We investigate the chemical substitution of group 5 into BaFe2As2 (122) iron arsenide, in the effort to understand why Fe-site hole doping of this compound (e.g., using group 5 or 6) does not yield bulk superconductivity. We find an increase in c-lattice parameter of the BaFe2As2 with the substitution of V, Nb, or Ta; the reduction in c predicts the lack of bulk superconductivity [1] that is confirmed here through transport and magnetization results. However, our spectroscopy measurements find a coexistence of antiferromagnetic and local superconducting nanoscale regions in V-122, observed for…
The thermal conductivity kappa of the iron-arsenide superconductor Ba1-xKxFe2As2 was measured for heat currents parallel and perpendicular to the tetragonal c axis at temperatures down to 50 mK and in magnetic fields up to 15 T. Measurements were performed on samples with compositions ranging from optimal doping (x = 0.34; Tc = 39 K) down to dopings deep into the region where antiferromagnetic order coexists with superconductivity (x = 0.16; Tc = 7 K). In zero field, there is no residual linear term in kappa(T) as T goes to 0 at any doping, whether for in-plane or inter-plane transport. This s…
(pi,pi)-electronic order in iron arsenide superconductors
金属中价电子的分布通常遵循离子晶格的对称性。这种分布的调制通常发生在这些电子相对于新的电子秩序不稳定时，例如自旋或电荷密度波。电子密度波已经在许多超导体家族中观察到[1-3]，并且通常被认为是超导性存在的必要条件[4]。最近的测量[5-9]似乎表明，铁磷属元素化物[10，11]的性质与不包括额外有序的能带结构计算非常一致，这意味着这些材料中的密度波和超导性之间没有关系[12-15]。在这里，我们报告了Ba 1-xKxFe 2 As 2的电子结构与那些能带结构计算[12-15]完全不一致，而是揭示了以（pi，pi）波矢量为特征的重构。这种电子秩序与超导性共存，并持续到室温。
When passing through a phase transition, electronic system saves energy by opening energy gaps at the Fermi level. Delineating the energy gap anisotropy provides insights into the origin of the interactions that drive the phase transition. Here, we report the angle-resolved photoemission spectroscopy (ARPES) study on the detailed gap anisotropies in both the tetragonal magnetic and superconducting phases in Sr$_{1-x}$Na$_x$Fe$_2$As$_2$. First, we found that the spin-density-wave (SDW) gap is strongly anisotropic in the tetragonal magnetic phase. The gap magnitude correlates with the orbital ch…
Doping dependence of heat transport in the iron-arsenide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$: from isotropic to strongly $k$-dependent gap structure
测量了砷化铁超导体Ba（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$的面内热导率$κ$的温度和磁场依赖性，该热导率低至$T \simeq 50$ mK，高至$H = 15$ T，作为Co浓度$x$的函数，范围为0.048 $ \leq x \leq $ 0.114。在零磁场下，在所有$x$处，$κ/T$中的可忽略的剩余线性项为$T \to 0$，这表明不存在零能准粒子，因此超导能隙在相图中的任何地方都没有$ab$平面中的节点。然而，$κ$的场依赖性揭示了具有掺杂$x$的超导带隙的系统演化，从欠掺杂状态下费米表面上的任何地方都大，如由$T \to 0$处的平坦$κ(H)$所证明的，到过掺杂状态下的强$k$依赖性，其中小磁场可以引起大的剩余线性项，这表明费米表面某处的能隙幅度存在一个深极小值。这表明超导能隙结构仅在反铁磁/正交相之外的费米表面周围具有强烈的$k$依赖的振幅。
In the temperature-concentration phase diagram of most iron-based superconductors, antiferromagnetic order is gradually suppressed to zero at a critical point, and a dome of superconductivity forms around that point. The nature of the magnetic phase and its fluctuations is of fundamental importance for elucidating the pairing mechanism. In Ba{1-x}KxFe2As2 and Ba{1-x}NaxFe2As2, it has recently become clear that the usual stripe-like magnetic phase, of orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal symmetry, near the critical point, between x = 0.24 and x = 0.28. Here…
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…
Recent observations of selective emergence (suppression) of superconductivity in the uncollapsed (collapsed) tetragonal phase of LaFe$_2$As$_2$ has rekindled interest in understanding what features of the band structure control the superconducting T$_c$. We show that the proximity of the narrow Fe-d$_{xy}$ state to the Fermi energy emerges as the primary factor. In the uncollapsed phase this state is at the Fermi energy, and is most strongly correlated and source of enhanced scattering in both single and two particle channels. The resulting intense and broad low energy spin fluctuations suppre…
NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors
我们提出了在Ba（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$和Ba（Fe $_{1-x}$ Cu $_x$）$_2$ As $_2$中作为温度、掺杂和磁场的函数的$^{75}$ As核磁共振自旋-晶格和自旋-自旋弛豫速率数据。弛豫曲线表现出广泛的弛豫率分布，与不均匀的玻璃态行为一致，高达100 K。掺杂和温度响应的动态不均匀性的宽度是类似的，通过弹性电阻测量测量的磁化率。我们认为，淬火的随机场耦合到一阶引起的自旋动力学中反映的一个玻璃。
