Itinerant magnetic excitations in antiferromagnetic CaFe2As2
S. O. Diallo, V. P. Antropov, T. G. Perring, C. Broholm, J. J. Pulikkotil, N. Ni, S. L. Bud'ko, P. C. Canfield, A. Kreyssig, A. I. Goldman, R. J. McQueeney
Neutron scattering measurements of the magnetic excitations in single crystals of antiferromagnetic CaFe2As2 reveal steeply dispersive and well-defined spin waves up to an energy of 100 meV. Magnetic excitations above 100 meV and up to the maximum energy of 200 meV are however broader in energy and momentum than the experimental resolution. While the low energy modes can be fit to a Heisenberg model, the total spectrum cannot be described as arising from excitations of a local moment system. Ab-initio calculations of the dynamic magnetic susceptibility suggest that the high energy behavior is dominated by the damping of spin waves by particle-hole excitations.
A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure ($P$) -dependent $^{115}$In nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh$_{0.5}$Ir$_{0.5}$In$_5$. These experiments reveal an antiferromagnetic (AF) QCP at $P_{\rm c}^{\rm AF}$ = 1.2 GPa where a dome o…
通过理论计算了解了CuFe $_2$ Ge $_2$的电子结构和磁性.能带结构显示出费米能级的大电子密度$N(E_F)$，表明磁性具有较强的巡游特征。费米面主要由二维片状结构组成，它们之间可能有很强的嵌套。磁基态沿$a$方向表现为铁磁，沿其它方向表现为反铁磁。结果表明，CuFe $_2$ Ge $_2$是一种反铁磁金属，具有铁基超导体的相似之处，如磁性具有明显的巡游特征，在费米能级处磁序与电子耦合.
We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of triangular-lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$, which was recently argued to host itinerant fermionic excitations, like a quantum spin liquid, above its antiferromagnetic phase transition temperature $T_{\rm N}$ = 0.148 K. In specific heat measurements, we confirm the peaks due to antiferromagnetic ordering when magnetic field $μ_0 H \leq$ 1 T, roughly consistent with previous work [N. Li $et$ $al.$, Nat. Commun. 11, 4216 (2020)]. However, in thermal conductivity measurement…
Spin fluctuations and pairing symmetry in A$_{x}$Fe$_{2-y}$Se$_{2}$: dual effect of the itinerant and the localized nature of electrons
在涨落交换近似下，研究了A $_{x}$ Fe $_{2-y}$ Se $_{2}$中的自旋涨落和对对称性.除了在位相互作用外，还考虑了次近邻反铁磁耦合$J_{2}$。我们发现电子的巡游性质和局域性质对描述最近的自旋涨落和对对称性的实验结果都很重要。特别地，小的$J_{2}$耦合可以将配对间隙从d波对称改变为s波对称。我们还研究了不同轨道的间隙函数的实空间结构，以便更深入地了解配对机制的性质。
Commensurate Itinerant Antiferromagnetism in BaFe2As2: 75As-NMR Studies on a Self-Flux Grown Single Crystal
我们报告的结果75砷核磁共振（NMR）实验上的自助熔剂生长的BaFe 2 As 2单晶。一个一级反铁磁（AF）转变附近135 K的NMR谱线的分裂，这是伴随着同时的结构转变，证明了突然大的变化的电场梯度张量在作为网站。NMR结果导致几乎唯一的条纹自旋结构在AF相。自旋-晶格弛豫速率的数据表明，在顺磁相中，随着温度的降低，各向异性的条纹型自旋涨落的发展。
We study the dynamical spin excitations of the one-dimensional $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropy by using quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation function. Using the transverse dynamic spin structure factor, we observe the quantum phase transition with a critical point between the topological Haldane gapped phase and the trivial phase. At the quantum critical point, we find a broad continuum characterized by the Tomonaga-Luttinger liquid similar to a $S=1/2$ Heisenberg antiferromagnetic chain. We furth…
Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe$_{1-x}$Se$_x$
最近已经证明，在铁硫属化物中通过中子散射测量的动态磁关联可以用短程关联的模型来描述，该短程关联的特征在于特定的{选择四自旋斑，其中适当的选择随着}母体材料被掺杂朝向超导性而改变。在这里，我们应用这样的模型来描述测量地图的磁散射作为二维波矢量的函数获得的最佳超导晶体FeTe $_{1-x}$ Se $_x$。我们发现，特征反铁磁波矢量的演变，发现在欠掺杂的硫族化物（在高温下）的双共线结构与条纹结构的反铁磁铁砷化物（在低温下）; {这些都可以描述相同的本地元格，但不同的元格间的相关性}。虽然低能磁谱权重的大小在所有温度下都很大，但它实际上在低温下有所减弱，其中载流子变得更加巡回。所观察到的自旋相关性的变化与电子散射率的急剧下降和冷却时的体散射响应的增长相关。最后，我们还提出了粉末中子衍射结果的晶格参数在FeTe $_{1-x}$ Se $_x$表明四面体键角趋于增加对冷却的理想值，在协议的增加屏蔽的晶体场更多的巡回电子和相应较小的分裂的Fe $3d$轨道。
The duality between localized and itinerant nature of magnetism in $5\textit{f}$ electron systems has been a longstanding puzzle. Here, we report inelastic neutron scattering measurements, which reveal both local and itinerant aspects of magnetism in a single crystalline system of UPt$_{2}$Si$_{2}$. In the antiferromagnetic state, we observe broad continuum of diffuse magnetic scattering with a resonance-like gap of $\approx$ 7 meV, and surprising absence of coherent spin-waves, suggestive of itinerant magnetism. While the gap closes above the Neel temperature, strong dynamic spin correlations…
To study how Andreev reflection (AR) is affected by itinerant antiferromagnetism, we perform $d$-wave AR spectroscopy with superconducting YBa$_2$Cu$_3$O$_{7-δ}$ on TiAu and on variously-oxidized Nb (NbO$_x$) samples. X-ray photoelectron spectroscopy is also used on the latter to measure their surface oxide composition. Below the Néel temperatures ($T_N$) of both TiAu and NbO$_x$, the conductance spectra show a dip-like structure instead of a zero-bias peak within the superconducting energy gap; for NbO$_x$, higher-oxidized samples show a stronger spectral dip at zero bias. These observations …
Unconventional superconductivity arises at the border between the strong coupling regime with local magnetic moments and the weak coupling regime with itinerant electrons, and stems from the physics of criticality that dissects the two. Unveiling the nature of the quasiparticles close to quantum criticality is fundamental to understand the phase diagram of quantum materials. Here, using resonant inelastic x-ray scattering (RIXS) and Fe-K$_β$ emission spectroscopy (XES), we visualize the coexistence and evolution of local magnetic moments and collective spin excitations across the superconducti…
Itinerant Nature of Spin-Density-Wave Order in Ruddlesden-Popper Nickelates
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）
Ultracold few fermionic atoms in needle-shaped double wells: spin chains and resonating spin clusters from microscopic Hamiltonians emulated via antiferromagnetic Heisenberg and t-J models
Itinerant effects and enhanced magnetic interactions in Bi-based multilayer cuprates
铜酸盐高温超导体表现出明显的趋势，其中超导转变温度$T_{\rm c}$随着晶体结构中CuO $_2$平面的数目$n$而增加。我们用Cu $L_3$ -边共振非弹性X射线散射（RIXS）比较了Bi $_{2+x}$ Sr $_{2-x}$ CuO $_{6+δ}$（Bi-2201）和Bi $_2$ Sr $_2$ Ca $_2$ Cu $_3$ O $_{10 + δ}$（Bi-2223）分别与$n=1$和$n=3$的磁激发谱。在反结区边界附近，我们发现Bi-2223的顺磁子能量显著高于Bi-2201，表明多层铜氧化物具有更强的有效磁交换作用，这为$T_{\rm c}$与Bi-2201的磁交换效应提供了可能的解释。$n$缩放。相反，节点方向表现出非常强的阻尼，几乎非色散激励。我们认为，这意味着在掺杂铜酸盐的磁性是部分巡回性质。
The spin excitations of the block-antiferromagnetic K$_{0.8}$Fe$_{1.6}$Se$_2$
利用文献中提出的有效自旋哈密顿量，研究了K $_{0.8}$ Fe $_{1.6}$ Se $_2$中新发现的块反铁磁态的自旋激发.有趣的是，除了通常的戈德斯通模式，还存在其他三个“光学”自旋波分支。这些自旋激发类似于晶体中的“光学声子”，每个晶胞中有一个以上的原子。我们计算了自旋波修正的有序矩和一致自旋磁化率。
