Ultrafast Melting of Spin Density Wave Order in BaFe$_{2}$As$_{2}$ Observed by Time- and Angle-Resolved Photoemission Spectroscopy with Extreme-Ultraviolet Higher Harmonic Generation
H. Suzuki, K. Okazaki, T. Yamamoto, T. Someya, M. Okada, K. Koshiishi, M. Fujisawa, T. Kanai, N. Ishii, M. Nakajima, H. Eisaki, K. Ono, H. Kumigashira, J. Itata… 展开作者
H. Suzuki, K. Okazaki, T. Yamamoto, T. Someya, M. Okada, K. Koshiishi, M. Fujisawa, T. Kanai, N. Ishii, M. Nakajima, H. Eisaki, K. Ono, H. Kumigashira, J. Itatani, A. Fujimori, S. Shin
Transient single-particle spectral function of BaFe$_{2}$As$_{2}$, a parent compound of iron-based superconductors, has been studied by time- and angle-resolved photoemission spectroscopy with an extreme-ultraviolet laser generated by higher harmonics from Ar gas, which enables us to investigate the dynamics in the entire Brillouin zone. We observed electronic modifications from the spin-density-wave (SDW) ordered state within $\sim$ 1 ps after the arrival of a 1.5 eV pump pulse. We observed optically excited electrons at the zone center above $E_{F}$ at 0.12 ps, and their rapid decay. After the fast decay of the optically excited electrons, a thermalized state appears and survives for a relatively long time. From the comparison with the density-functional theory band structure for the paramagnetic and SDW states, we interpret the experimental observations as the melting of the SDW. Exponential decay constants for the thermalized state to recover back to the SDW ground state are $\sim$ 0.60 ps both around the zone center and the zone corner.
Theoretical study on the anisotropic electronic structure of antiferromagnetic BaFe$_2$As$_2$ and Co-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ seen by angle-resolved photoemission
用一步模型计算方法研究了铁磷属元素化物原型化合物BaFe $_2$ As $_2$和Ba（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$在低温反铁磁相中的角分辨光电发射中所表现出的强面内各向异性.完全相对论计算是基于Korringa-Kohn-Rostoker-Green函数方法结合相干势近似合金理论，以一种可靠的方式来解释Co取代Fe位引起的无序。计算的结果可以直接与实验光谱的解孪晶单晶。人们发现非常好的协议与实验，可以揭示所有的电子结构的功能，有助于在平面各向异性。特别是局域密度近似可以捕捉到大多数的相关效应的调查系统，而不需要更先进的技术。此外，可以几乎连续地跟踪Ba（Fe $x$ Co $_x$）$_2$ As $_2$中随Co浓度增加的各向异性的演变。结果也被用来讨论表面效应，它是可能的，以确定明确的签名，以得出不同类型的表面终止。
Polarization-Dependent Three-Dimensional Angle-Resolved Photoemission Spectroscopy of BaFe$_{1.8}$Co$_{0.2}$As$_{2}$
我们利用偏振和光子能量相关的角度分辨光电子能谱研究了一种稍过掺杂的铁磷属元素化物超导体BaFe $_{1.8}$ Co $_{0.2}$ As $_{2}$的三维电子结构，包括布里渊区中心的轨道特征.观察到具有$d_{xz/yz}$和$d_{xy/x^2-y^2}$轨道的两个空穴费米面（FS），但是没有出现根据自旋涨落超导机制理论具有节点的$d_{z^2}$空穴FS。这些结果表明，在区域中心的孔FS处不会出现节点。
Orbital character variation of the Fermi surface and doping dependent changes of the dimensionality in BaFe2-xCoxAs2 from angle-resolved photoemission spectroscopy
Electronic structure of heavily electron-doped BaFe$_{1.7}$Co$_{0.3}$As$_2$ studied by angle-resolved photoemission
我们对重电子掺杂非超导BaFe $_{1.7}$ Co $_{0.3}$ As $_2$进行了高分辨角分辨光电子能谱研究。我们发现在空穴掺杂的超导体Ba $_{0.6}$ K $_{0.4}$ Fe $_2$ As $_2$中观察到的两个空穴费米面口袋在该化合物中不存在或非常小，而在M点处的两个电子口袋由于Co替代的电子掺杂而显著膨胀。非SC和SC样品的费米面的比较表明，通过反铁磁波矢连接的空穴和电子口袋的共存是实现铁基超导体的超导性机制的必要条件。
A high resolution, hard X-ray photoemission investigation of BaFe$_2$As$_2$: moderate influence of the surface and evidence for a low degree of Fe 3d - As 4p hybridization of the near-E$_F$ electronic states
本文报道了用硬X射线辐照MFe $_2$ As $_2$磷族元素化物高温超导体族钡母体化合物解理单晶的光电子能谱数据。利用硬X射线激发时增加的体积灵敏度，并比较结果与在常规VUV光发射激发能下所取的数据，结果表明，BaFe $_2$作为$_2$解理表面提供了一个静电环境，这是稍微不同的散装，最有可能的形式修改后的马德隆电位。然而，由于数据反对不同的表面掺杂水平，并且光谱中与表面相关的特征决不像在YBa $_2$ Cu $_3$ O $_x$等系统中所见的那样占主导地位，因此我们可以得出结论，巡游的近E $_F$电子态几乎不受解理表面存在的影响。此外，利用强烈的变化，在光电离横截面之间的Fe和As状态在整个宽的光子能量范围内采用，它表明，铁3d和砷4p价带之间的能量重叠的程度是特别小的费米能级，这只能意味着一个非常低的程度的Fe 3d和As 4p状态附近和E $_F$之间的杂交。因此，在这组材料中的电荷载流子的巡回性主要涉及Fe 3d-Fe 3d重叠积分与Fe 3d-As 4p跳跃参数的最佳次要作用，并且在掺杂时支持超导性的状态基本上是Fe 3d特征。
Spin gap and magnetic resonance in superconducting BaFe$_{1.9}$Ni$%_{0.1}$As$_{2}$
本文用中子能谱方法研究了BaFe $_{1.9}$ Ni $_{0.1}$ As $_{2}$（$T_{c}=20$ K）超导体中磁激发的性质。在$T_{c}$以上，激发是无隙的，并以母体化合物的相称反铁磁波矢量为中心，而强度沿c轴呈现正弦调制。当进入超导状态时，自旋能隙逐渐打开，其幅度跟踪通过角分辨光电能谱观察到的超导能隙的$T$依赖性。自旋能隙和磁共振能都与温度\textit{and}波矢有关，但它们的比值在不确定度范围内是相同的。这些结果表明，自旋共振是一种与电子配对和超导电性有关的单重态-三重态激发。
Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. While extensive photoemission results have been obtained, the surface complexity of 122 caused by its charge-non-neutral surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$, the surface-induced spectral broadening is strongly suppressed, and hence the coherent spectra that reflect the intrinsic bulk electronic state recover.…
Ultrafast modulation of the chemical potential in BaFe$_2$As$_2$ by coherent phonons
利用时间分辨和角度分辨极紫外光电子能谱研究了BaFe $_2$ As $_2$在高对称点$Γ$和$M$附近的电子结构动力学.观察到费米能级在$A_{1g}$（As）声子模频率处的全局振荡。有人认为，这种行为反映了调制的有效化学势在光激发的表面区域，所产生的高灵敏度的能带结构附近的费米能级的$A_{1g}$声子模式与低电子扩散率垂直的层。这一结果为铁磷属化合物的电子性质调控提供了一种新的途径：有效化学势的相干控制。结果进一步表明，在弱层间耦合材料的超快电子结构动力学中，需要考虑有效化学势的平衡时间。
We determine the work functions of the iron arsenic compounds $A$Fe$_2$As$_2$ ($A=\mathrm{Ca, Ba, Cs}$) using photoemission spectroscopy to be 2.7 eV for CaFe$_2$As$_2$, 1.8 eV for BaFe$_2$As$_2$, and 1.3 eV for CsFe$_2$As$_2$. The work functions of these 122 iron-based superconductors track those of the elementary metal $A$ but are substantially smaller. The most likely explanation of this observation is that the cleaving surface exposes only half an $A$-layer. The low work function and good photoemission cross section of BaFe$_2$As$_2$ and CsFe$_2$As$_2$ enable photoemission even from a comm…
Complete Fermi surface in BaFe$_2$As$_2$ observed via Shubnikov-de Haas oscillation measurements on detwinned single crystals
结果表明，BaFe $_2$ As $_2$反铁磁相的费米面（FS）由一个空穴和两个电子袋组成，它们都是三维的封闭的，与角分辨光电子能谱所观察到的FS形成鲜明对比.载波补偿和索末菲系数的考虑排除了未观察到的FS口袋的存在。一个标准的能带结构计算合理占所观察到的FS，尽管高估了有序矩。质量增强，即有效质量与能带质量之比，为2- 3。
We have performed an angle-resolved photoemission spectroscopy study of BaCr$_2$As$_2$, which has the same crystal structure as BaFe$_2$As$_2$, a parent compound of Fe-based superconductors. We determine the Fermi surface of this material and its band dispersion over 5 eV of binding energy. Very moderate band renormalization (1.35) is observed for only two bands. We attribute this small renormalization to enhanced direct exchange as compared to Fe in BaFe$_2$As$_2$, and to a larger contribution of the $e_g$ orbitals in the composition of the bands forming the Fermi surface, leading to an effec…
Orbital-Selective Band Structure Evolution in BaFe$_{2-x}$M$_x$As$_2$ (M = Cr, Co, Cu, Ru and Mn) Probed by Polarization-Dependent ARPES
Université de Sherbrooke（舍布鲁克大学）；European Synchrotron Radiation Facility（欧洲同步辐射装置）；UNICAMP（坎皮纳斯州立大学）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Universidade de São Paulo（圣保罗大学）
We have investigated the electronic structure of $\mathrm{Sr}_{1-y}\mathrm{Ca}_{y}\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($x$ = 0.25, $y$ = 0.08) by means of angle-resolved photoemission spectroscopy. From the comparison with the results of $\mathrm{BaFe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$, the effects of smaller structural anisotropy ($c/a$) on the Fermi surfaces (FSs) and the gap structures are discussed. The observed FSs have three dimensional shapes. One of the hole FSs is strongly warped between the $Γ$ and $Z$ points, and the innermost FS observed …
Unusual Fermi surface nesting in parent compounds of iron arsenic high temperature superconductors revealed by Angle Resolved Photoemission Spectroscopy
Hole doping and electronic correlations in Cr-substituted BaFe$_{2}$As$_{2}$
Universidade de São Paulo（圣保罗大学）；European Synchrotron Radiation Facility（欧洲同步辐射装置）；UNICAMP（坎皮纳斯州立大学）；Université de Fribourg（弗里堡大学）；Universidade Federal de Minas Gerais（米纳斯吉拉斯联邦大学）；Ames Laboratory, U.S. DOE（美国能源部艾姆斯实验室）
Disorder-induced damping of spin excitations in Cr-doped BaFe$_2$As$_2$
European Synchrotron Radiation Facility（欧洲同步辐射装置）；Instituto de Física, Universidade de São Paulo（圣保罗大学物理研究所）；Institut Quantique and Département de Physique, Université de Sherbrooke（舍布鲁克大学量子研究所与物理系）；Fakultät für Chemie und Mineralogie, Universität Leipzig（莱比锡大学化学与矿物学院）；School of Chemistry and Chemical Engineering, University of Surrey（萨里大学化学与化学工程学院）；Diamond Light Source（钻石光源）；Instituto de Física “Gleb Wataghin”, UNICAMP（坎皮纳斯大学格莱布·瓦塔金物理研究所）；Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg（弗里堡大学物理系与弗里堡纳米材料中心）；Photon Science Division, Paul Scherrer Institut（保罗谢尔研究所光子科学部）
The main driven force of the electronic nematic phase in iron-based superconductors is still under debate. Here, we report a comprehensive study on the nematic fluctuations in a non-superconducting iron pnictide system BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$ by electronic transport, angle-resolved photoemission spectroscopy (ARPES) and inelastic neutron scattering (INS) measurements. Previous neutron diffraction and transport measurements suggested that the collinear antiferromagnetism persists to $x=0.8$, with similar Néel temperature $T_N$ and structural transition temperature $T_s$ around …
We investigate the transient electronic structure of BaFe2As2, a parent compound of iron-based superconductors, by time- and angle-resolved photoemission spectroscopy. In order to probe the entire Brillouin zone, we utilize extreme ultraviolet photons and observe photoemission intensity oscillation with the frequency of the A1g phonon which is antiphase between the zone-centered hole Fermi surfaces (FSs) and zone-cornered electron FSs. We attribute the antiphase behavior to the warping in one of the zone-centered hole FSs accompanying the displacement of the pnictogen height, and find that thi…
Nematicity is ubiquitous in electronic phases of high transition temperature superconductors, particularly in iron-based superconductors (IBSCs). Order parameter that characterizes the nematic phase has been investigated in momentum space, but its real-space arrangement remains largely unclear. We use linear dichroism (LD) in low-temperature laser-photoemission electron microscope to map out the nematic order parameter of nonmagentic FeSe and antiferromagnetic BaFe2(As0.87P0.13)2. In contrast to the structural domains that have atomic-scale domain walls, the LD patterns in both materials show …
