Suppression of the structural phase transition and lattice softening in slightly underdoped Ba(1-x)K(x)Fe2As2 with electronic phase separation
D. S. Inosov, A. Leineweber, Xiaoping Yang, J. T. Park, N. B. Christensen, R. Dinnebier, G. L. Sun, Ch. Niedermayer, D. Haug, P. W. Stephens, J. Stahn, C. T. Li… 展开作者
D. S. Inosov, A. Leineweber, Xiaoping Yang, J. T. Park, N. B. Christensen, R. Dinnebier, G. L. Sun, Ch. Niedermayer, D. Haug, P. W. Stephens, J. Stahn, C. T. Lin, O. K. Andersen, B. Keimer, V. Hinkov
We present x-ray powder diffraction (XRPD) and neutron diffraction measurements on the slightly underdoped iron pnictide superconductor Ba(1-x)K(x)Fe2As2, Tc = 32K. Below the magnetic transition temperature Tm = 70K, both techniques show an additional broadening of the nuclear Bragg peaks, suggesting a weak structural phase transition. However, macroscopically the system does not break its tetragonal symmetry down to 15 K. Instead, XRPD patterns at low temperature reveal an increase of the anisotropic microstrain proportionally in all directions. We associate this effect with the electronic phase separation, previously observed in the same material, and with the effect of lattice softening below the magnetic phase transition. We employ density functional theory to evaluate the distribution of atomic positions in the presence of dopant atoms both in the normal and magnetic states, and to quantify the lattice softening, showing that it can account for a major part of the observed increase of the microstrain.
The normal state of optimally doped cuprates is dominated by the "strange metal" phase that shows a linear temperature ($T$) dependence of the resistivity persisting down to the lowest $T$. For underdoped cuprates this behavior is lost below the pseudogap temperature $T^*$, where Charge Density Waves (CDW) together with other intertwined local orders characterize the ground state. Here we show that the $T$-linear resistivity of highly strained, ultrathin and underdoped YBa$_2$Cu$_3$O$_{7-δ}$ films is restored when the CDW amplitude, detected by Resonant Inelastic X-ray scattering, is suppresse…
Suppression of low-energy longitudinal spin-excitations in Co-underdoped BaFe2As2
利用极化非弹性中子散射实验研究了Co欠掺杂BaFe $_2$ As $_2$的正常相和超导相的磁激发，该样品具有反铁磁有序和超导电性共存的特点.在正常状态下，反铁磁有序导致在所有三个自旋方向上的加宽的自旋隙开口，这让人想起纯反铁磁BaFe $_2$ As $_2$中的磁响应。特别是纵向激励表现出一个大的差距。在超导态中，我们发现了两种不同的共振激发，它们在自旋空间中都是各向异性的，并且都不出现在纵向极化通道中。这种行为与之前在接近最佳或更高掺杂的样品上的极化中子结果形成对比。由反铁磁序引起的纵向涨落的能隙似乎比超导能隙的两倍大得多，足以抑制与超导态的任何相互作用。这种被抑制的低能纵向涨落权重可以解释低掺杂BaFe $_2$ As $_2$中超导转变温度的降低，并表明反铁磁性和超导性在局部共存。
Competition between orthorhombic and re-entrant tetragonal phases in underdoped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ probed by the response to controlled disorder
利用2.5 MeV电子低温辐照研究了空穴掺杂Ba $_{1-x}$ K $_x$ Fe $_2$ As $_2$中存在于$x=$ 0.25附近的条状${\rm C_2}$和四元${\rm C_4}$反铁磁相之间的竞争.在该范围之外的附近成分中，在$x=$ 0.22和$x=$ 0.19处，伴随的正交/条纹反铁磁转变$T_{\rm C2}$和超导转变$T_{\rm c}$的温度都被添加的无序以约0.1 K/ $μΩ$ cm的类似速率单调抑制，如通过使用电阻率变化作为散射速率的本征测量所揭示的。与此形成鲜明对比的是，在$x=$ 0.25时发现在速率为0.24 K/ $μΩ\cdot$ cm时对${\rm C_4}$相的快速抑制。此外，${\rm C_4}$相的这种抑制伴随着${\rm C_2}$相的不寻常的无序诱导的稳定化，这通过电阻率和比热测量来确定。${\rm C_4}$相的抑制率明显高于Ni掺杂的CaKFe $_4$ As $_4$中自旋涡旋相的抑制率（0.16 K/ $μΩ$ cm）。
Infrared probe of the gap evolution across the phase diagram of Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$
我们测量了超导单晶Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$的光学电导率，$x$范围从0.40（最佳掺杂，$T_c = 39$ K）到0.20（欠掺杂，$T_c = 16$ K），其中磁序与超导性共存。在正常状态下，低频光学电导率可以由非相干的宽Drude分量和相干的窄Drude分量来描述：宽Drude分量与掺杂无关，而窄Drude分量在重欠掺杂化合物中显示出强散射。在超导状态下，冷凝物的形成导致低频抑制的光学电导率谱权重。在重欠掺杂区，超流密度被显著抑制，未成对载流子的重量迅速增加。我们将这些结果归因于整个相图中超导能隙的变化，这可能表明由于欠掺杂Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$中磁性和超导性之间的强烈相互作用而导致的无结转变。
1/8 Doping Anomalies and Oxygen Vacancies in Underdoped Superconducting Cuprates
讨论了几种铜氧化物超导体的热导率（$κ$）随温度和掺杂的变化。在YBa $_2$ Cu $_3$ O $_{6+x}$和Hg铜酸盐中观察到的1/8掺杂附近的正常状态$κ$和$κ$在$T_c$的斜率变化的抑制值，分别归因于局部晶格畸变和超导冷凝物的抑制。这两种现象都被认为是由局部平面孔的小区域引起的，可能是相分离的表现。结果表明，$κ$的相行为反映了条纹动力学和氧空位团簇对1/8掺杂异常条纹的钉扎。
Fragile charge order in the non-superconducting ground state of the underdoped high temperature superconductors
几十年来，空穴欠掺杂氧化铜超导体的正常态一直是一个谜。测量一个小的费米面的量子振荡抑制超导高施加磁场，连同互补的光谱测量的空穴欠掺杂的氧化铜超导体，点从电荷顺序在YBa 2 Cu 3 O 6 +x的节点电子口袋。在这里，我们报告的量子振荡测量密切相关的化学计量材料YBa 2Cu 4 O 8，这揭示了类似的费米表面性质YBa 2Cu 3 O 6 +x，尽管没有在相同的光谱技术，如X-射线衍射，揭示在YBa 2Cu 3 O 6 +x的电荷顺序签名。费米面重建YBa 2Cu 4 O 8建议发生从磁场增强的电荷秩序，呈现脆弱的零磁场，因为它的潜在的非常规对称性，和/或其发生作为一个附属的更强大的潜在的电子相关性。
Nematic correlation length in iron-based superconductors probed by inelastic x-ray scattering
向列性普遍存在于高$T_c$超导体的电子相中，特别是在Fe基体系中。我们使用非弹性X射线散射提取的温度依赖的温度相关长度$ξ$从FeSe，欠掺杂Ba（Fe $_{0.97}$ Co $_{0.03}$）$_2$作为$_2$和最佳掺杂Ba（Fe $_{0.94}$ Co $_{0.06}$）$_2$作为$_2$的声学声子模式的异常软化。在所有情况下，我们发现，$ξ$是很好地描述了一个幂律$(T-T_0)^{-1/2}$在很宽的温度范围内延伸。我们将这种平均场行为和扩展的波动机制归因于相当大的线弹性耦合，这可能对超导电性有害。
We performed temperature- and doping-dependent high-resolution Raman spectroscopy experiments on YBa$_2$Cu$_3$O$_{7-δ}$ to study $B$$_{\rm 1g}$ phonons. The temperature dependence of the real part of the phonon self-energy shows a distinct kink at $T=T_{\rm B1g}$ above $T$$_{\rm c}$ due to softening, in addition to the one due to the onset of the superconductivity. $T$$_{\rm B1g}$ is clearly different from the pseudogap temperature with a maximum in the underdoped region. The region between $T$$_{\rm B1g}$ and $T$$_{\rm c}$ resembles that of superconducting fluctuation or charge density wave o…
Strongly suppressed superconducting proximity effect and ferromagnetism in trilayers of $\rm Bi_2Se_3$ / $\rm SrRuO_3$ / underdoped $\rm YBa_2Cu_3O_x$: A possible new platform for Majorana nano-electronics
Electronic nematicity in iron pnictide materials has been extensively studied by various experimental techniques, yet its heat capacity anomaly at the phase transition has not been examined quantitatively. In this work we review the thermodynamic description of nematicity in $Ba(Fe_{1-x}Co_{x})_{2}As_{2}$ using the Landau free energy, which defines the behavior of three thermodynamic quantities: the structural orthorhombicity that develops below the nematic transition, the softening shear modulus above the transition, and the discontinuous heat capacity at the transition. We derive a quantitat…
Interplane resistivity of underdoped single crystals (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$, $0 \leq x<0.34$
测量了空穴掺杂砷化铁超导体（Ba $_{1-x}$ K $_x$）Fe $_2$ As $_2$在从母体化合物到最佳掺杂$T_c\approx 38~K$，$0\leq x \leq 0.34$的掺杂范围内随温度变化的面间电阻率$ρ_c(T)$。对从FeAs熔剂中生长的高质量单晶进行了测量。在$T_{SM}$处的耦合磁性/结构转变导致在具有$T_c <$ 26~K（$x <0.25$）的样品中$ρ_c(T)$在冷却时明显加速减少。空穴掺杂材料的这种减少与电子掺杂的Ba（Fe $_{1-x}$ Co $_x$）Fe $_2$ As $_2$和等电子取代的BaFe $_2$（As $_{1-x}$ P $_x$）$_2$中$ρ_c(T)$的增加形成显著对比。$T_{SM}$随掺杂而急剧下降，当$T_c$从约25增加到27时，从$T_s$ =71~ K下降到零。$ρ_c(T)$变为$T$ -接近最佳掺杂的线性。在母体BaFe $_2$ As $_2$中发现的在大约$T_{max} \sim$ 200~K处的$ρ_c(T)$中的宽交叉最大值移动到掺杂$x$ =0.34的更高温度$\sim$ 250~K。最大值显示出与温度相关的面内电阻率$ρ_a(T)$中发现的宽交叉特征的明确相关性。$T_{max}$在（Ba $_{1-x}$ K $_x$）Fe $_2$ As $_2$中的掺杂演变与在B…
Intrinsic phase fluctuation and superfluid density in doped Mott insulators
Institute for Advanced Study, Tsinghua University（清华大学高等研究院）；French American Center for Theoretical Science, CNRS（法国美国理论科学中心，法国国家科学研究中心）；KITP, Santa Barbara, California（加州大学圣塔芭芭拉分校理论物理卡弗里研究所）；Kavli Institute for Theoretical Physics, University of California, Santa Barbara（加州大学圣塔芭芭拉分校卡弗里理论物理研究所）
Gapless spin excitations in superconducting La$_{2-x}$Ca$_{1+x}$Cu$_{2}$O$_{6}$ with $T_c$ up to 55 K
我们报告非弹性中子散射的双层铜酸盐家庭La $_{2-x}$ Ca $_{1+x}$ Cu $_{2}$ O $_{6+δ}$，包括两个晶体超导（在45和55 K的转变）在含氧气氛中的高压退火单晶。非超导晶体中的磁激发具有与弱空穴掺杂铜氧化物类似的温度依赖性。在超导晶体中，随着温度的升高，磁谱权重几乎均匀地受到抑制;特别是，没有自旋间隙或“共振”峰的迹象。这不同于在许多最佳掺杂的铜酸盐中看到的温度依赖性，但类似于在某些欠掺杂的铜酸盐中看到的行为。我们讨论了它与对密度波超导的可能联系。
Effects of high-pressure synthesis on phase formation and superconducting properties of PrFeAsO1-xFx
Institute of High Pressure Physics (IHPP), Polish Academy of Sciences（波兰科学院高压物理研究所）；Faculty of Physics, Warsaw University of Technology（华沙理工大学物理学院）；Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所）
We undertake a detailed high-resolution diffraction study of a novel plain band insulator, La$_2$MgO$_4$, which may be viewed as a structural surrogate system of the undoped end-member of the high-T$_c$ superconductors, La$_{2-x-y}$A$^{2+}_x$RE$^{3+}_y$CuO$_{4}$ (A = Ba, Sr, RE= Rare Earth). We find that La$_2$MgO$_4$ exhibits the infamous low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase transition that has been linked to the suppression of superconductivity in a variety of underdoped cuprates, including the well known La$_{2-x}$Ba$_{x}$CuO$_4$ ($x=0.125$). Furtherm…
Effects of electron irradiation on resistivity and London penetration depth of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($x \leq$ 0.34) iron - pnictide superconductor
用2.5 MeV电子以高达5.2 $\times$ 10 $^{19}$电子/cm $^2$的剂量辐照，在Ba $_{1-x}$ K $_x$ Fe $_2$单晶中引入点状缺陷。（$T_c=$ 14 K），$x=$ 0.26（$T_c=$ 32 K）和0.34（$T_c=$ 39 K）通过探测非磁散射对电阻率$ρ(T)$和伦敦穿透深度$ λ(T)$的影响来研究超导间隙结构。对于所有的组合物，照射抑制超导转变温度，$T_c$和增加的电阻率。$λ(T)$的低温行为最好用幂律函数$Δλ(T) = A(T/T_c)^n$来描述.虽然$T_c$的实质性抑制支持$s_{\pm}$配对机制，但在接近最佳掺杂的样品中，$x=$ 0.26和0.34，指数$n$保持高（$n \geq 3$），表明稳健的全超导带隙。对于表现出超导性和长程磁性共存的$x=$ 0.19组合物，$T_c$的抑制快得多，并且指数$n$朝向$n$ = 2的脏极限降低。在该样品中，照射还抑制了结构/磁性转变的温度，$T_{sm}$，从103 K到98 K，与磁序的巡回性质一致。我们的研究结果表明，欠掺杂的组合物，特别是在共存制度是最容易受到非磁散射，并意味着在多频带Ba $_{1-x}$ K $_x$ Fe $_2$作为$_2$超导体，带间带内配对强度的比率，以及相关的间隙各向异性，增加后，从最佳掺杂的偏离。
Magnetic field-dependence of the basal-plane superconducting anisotropy in YBa2Cu4O8 from small-angle neutron scattering measurements of the vortex lattice
我们报道了欠掺杂YBa $_{2}$ Cu $_{4}$ O $_{8}$（Y 124）超流密度的基面各向异性的研究，显示了CuO $_{2}$面和完全占据的CuO链的影响.从涡旋晶格的小角中子散射测量，我们可以推断温度（$T$）范围$T=$ 1.5 K至$T_{\rm c}$和磁感应强度$B$从0.1 T至6 T的超导（SC）性质。我们发现，沿\textbf{a}的超流密度有一个简单的$d$波T-依赖。然而，沿着\textbf{b}（链方向），超流密度随着$T$和场的增加而下降得更快。这强烈地暗示了邻近效应诱导的CuO链中的超导电性的抑制。此外，我们的研究结果不支持一个共同的框架，低场平面SC响应在Y 124和相关的YBa $_{2}$ Cu $_{3}$ O $_{7}$，也表明，任何磁场诱导的电荷密度波秩序在Y 124只存在于6 T以上的领域。
