我们进行了$^{75}$ As和$^{23}$ Na核磁共振(NMR)测量的单晶NaFe $_{0.9835}$ Co $_{0.0165}$ As和发现微观共存的超导性与两个组件的自旋密度波(SDW)。用$^{23}$ Na NMR测量了局部磁场的空间分布。发现SDW与具有磁矩的主要组分($\sim0.2\,μ_B$ /Fe)和具有磁矩的较小组分($\sim0.02\,μ_B$ /Fe)不相称。自旋晶格弛豫实验表明,这种共存发生在微观水平。
英文摘要:
We have performed $^{75}$As and $^{23}$Na nuclear magnetic resonance (NMR) measurements on a single crystal of NaFe$_{0.9835}$Co$_{0.0165}$As and found microscopic coexistence of superconductivity with a two-component spin density wave (SDW). Using $^{23}$Na NMR we measured the spatial distribution of local magnetic fields. The SDW was found to be incommensurate with a major component having magnetic moment ($\sim0.2\,μ_B$/Fe) and a smaller component with magnetic moment ($\sim0.02\,μ_B$/Fe). Spin lattice relaxation experiments reveal that this coexistence occurs at a microscopic level.
We use inelastic neutron scattering to study the fate of the two spin resonance modes in underdoped superconducting NaFe$_{1-x}$Co$_x$As ($x=0.0175$) under applied magnetic fields. While an applied in-plane magnetic field of $B=12$ T only modestly suppresses superconductivity and enhances static antiferromagnetic order, the two spin resonance modes display disparate responses. The spin resonance mode at higher energy is mildly suppressed, consistent with the field effect in other unconventional superconductors. The spin resonance mode at lower energy, on the other hand, is almost completely su…
We use neutron scattering to study the electron-doped superconducting NaFe$_{0.985}$Co$_{0.015}$As ($T_c=14$ K), which has co-existing static antiferromagnetic (AF) order ($T_N=31$ K) and exhibits two neutron spin resonances ($E_{r1}\approx 3.5$ meV and $E_{r2}\approx 6$ meV) at the in-plane AF ordering wave vector ${\bf Q}_{\rm AF}={\bf Q}_{1}=(1,0)$ in reciprocal space. In the twinned state below the tetragonal-to-orthorhombic structural transition $T_s$, both resonance modes appear at ${\bf Q}_{1}$ but cannot be distinguished from ${\bf Q}_{2}=(0,1)$. By detwinning the single crystal with u…
Why phase diagrams of different underdoped cuprates are remarkably different? Disorder versus bilayer
与广泛接受的观点相反,La $_{2-x}$ Sr $_x$ CuO $_4$和YBa $_2$ Cu $_3$ O $\rm_{6+y}$的相图尽管相似,但却明显不同。导电性质和公度/非公度自旋有序性质都有很大的不同。有人认为,在YBCO的作用是微不足道的,而双层结构是至关重要的。另一方面,在LSCO中,内在无序在很大程度上驱动系统的性质。所开发的方法解释了系统的低温磁性。最重要的一点是关于无公度自旋排序的差异,包括无公度螺距的差异。分析表明,超导性与无公度自旋有序密切相关。
Neutron spin resonance, a collective magnetic excitation coupled to superconductivity, is one of the most prominent features shared by a broad family of unconventional superconductors including copper oxides, iron pnictides, and heavy fermions. In this work, we study the doping evolution of the resonances in NaFe$_{1-x}$Co$_x$As covering the entire superconducting dome. For the underdoped compositions, two resonance modes coexist. As doping increases, the low-energy resonance gradually loses its spectral weight to the high-energy one but remains at the same energy. By contrast, in the overdope…
We use unpolarized and polarized neutron scattering to study the temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe$_{0.9785}$Co$_{0.0215}$As, with coexisting superconductivity ($T_{\rm c}\approx19$ K) and weak antiferromagnetic order ($T_{\rm N}\approx30$ K, ordered moment $\approx0.02$ $μ_{\rm B}$/Fe). A single spin resonance mode with intensity tracking the superconducting order parameter is observed, although energy of the mode only softens slightly on approaching $T_{\rm c}$. Polarized neutron scattering reveals that the single resonan…
Reconstructed Fermi surface and quantum oscillation of doped resonating valence bond state with incommensurate charge order in underdoped cuprates
最近的实验已经揭示了欠掺杂铜氧化物(如YBa $_2$ Cu $_3$ O $_{6+δ}$和HgBa $_2$ CuO $_{4+δ}$)中赝能隙区的非公度电荷密度波(CDW)。然而,它与pseudogap的关系仍然存在争议。在这项工作中,我们采取的掺杂共振价键(RVB)状态和CDW秩序的唯象综合。从Yang-Rice-Zhang Green函数对掺杂RVB态的解释[Phys. Rev. B { \bf 73},174501(2006)]出发,其中Fermi表面被反节点RVB能隙部分截断为四个节孔状Fermi口袋,我们证明了连接Fermi弧尖端的波矢处的CDW阶(热点)诱导费米表面重构,产生类电子费米口袋($α$轨道)和新的类空穴费米口袋($β$轨道)。$α$轨道是通过在热点处连接费米弧而形成的,并且它在量子振荡傅里叶光谱中占据主导地位,而$β$轨道是通过连接原始空穴的外部补丁而形成的,其光谱权重小得几乎为零。从磁场中的态密度振荡中提取了这些轨道所围成的区域,定量地与实验相符合。
Incommensurate spin dynamics in underdoped cuprate perovskites
基于投影算符形式和Cu-O面的t-J模型,对正常态铜酸盐钙钛矿中观察到的非公度磁响应进行了解释。与实验结果一致,计算得到的极化率最大值的色散具有两条抛物线的形状,向上和向下的分支会聚在反铁磁波矢处。最大值分别位于下抛物线和上抛物线中的动量$({1/2},{1/2}\pmδ)$、$({1/2}\pmδ,{1/2})$和$({1/2}\pmδ,{1/2}\pmδ)$、$({1/2}\pmδ,{1/2}\mpδ)$处。上抛物线反映了本地化的铜自旋的磁激发的分散,而下抛物线出现由于在反铁磁波矢量的自旋-激发阻尼下降。对于中度掺杂,这种下降源于自旋激发和热点附近的空穴之间的相互作用的弱点。的磁化率的频率依赖性强烈依赖于孔的带宽和阻尼,并从观察到的形状不同的YBa $_2$铜$_3$ O $_{7-y}$的固有的La $_{2-x}$ Sr $_x$ CuO $_4$。
In copper-oxide and iron-based high temperature (high-$T_{\rm c}$) superconductors, many physical properties exhibit in-plane anisotropy, which is believed to be caused by a rotational symmetry-breaking nematic order, whose origin and its relationship to superconductivity remain elusive. In many iron-pnictides, a tetragonal-to-orthorhombic structural transition temperature $T_{\rm s}$ coincides with the magnetic transition temperature $T_{\rm N}$, making the orbital and spin degrees of freedom highly entangled. NaFeAs is a system where $T_{\rm s}$ = 54 K is well separated from $T_{\rm N}$ = 42…
Understanding the interplay between nematicity, magnetism and superconductivity is pivotal for elucidating the physics of iron-based superconductors. Here we use neutron scattering to probe magnetic and nematic orders throughout the phase diagram of NaFe$_{1-x}$Ni$_x$As, finding that while both static antiferromagnetic and nematic orders compete with superconductivity, the onset temperatures for these two orders remain well-separated approaching the putative quantum critical points. We uncover local orthorhombic distortions that persist well above the tetragonal-to-orthorhombic structural tran…
Strong-Coupling Superconductivity in NaFe$_{1-x}$Co$_x$As: the Eliashberg Theory and Beyond
通过比热测量研究了NaFe $_{1-x}$ Co $_x$ As体系的正常态和超导性质。无论是正常状态的索末菲系数和超导凝聚能强烈抑制在欠掺杂和重掺杂样品。低温电子比热可以用单能隙或双能隙BCS型函数很好地拟合。比率$γ_NT_c^2/H_c^2(0)$可以很好地将中子自旋共振与标准Eliashberg模型中的玻色子联系起来。然而,接近最佳掺杂的$ΔC/T_cγ_N$的值大于模型可以获得的最大值。我们的研究结果表明,高$T_c$的铁基超导体的超导电性可以理解的玻色子交换机制的框架内,但可能需要显着的修改,以考虑有限温度的属性。
Magnetic quantum oscillations and multiple holon pockets in underdoped YBa$_2$Cu$_3$O$_{6+y}$
研究表明,轻掺杂$_2$ $_3$ O $_{6+y}$具有多个不同面积的空穴,导致多个频率的磁量子振荡.使用中子散射数据的无公度自旋排序,我们确定这些领域,产生的频率与实验吻合良好。磁量子振荡中观察到的有效质量的发散表明在氧含量$y\approx 0.48$的量子相变。我们认为,过渡是准静态的理论预测和中子散射中观察到的无公度磁序的发病。
In the present work we explain the hour-glass magnetic dispersion in underdoped cuprates. The dispersion arises due to the Lifshitz-type magnetic criticality. Superconductivity also plays a role, but the role is secondary. We list six major experimental observations related to the hour-glass and explain all of them. The theory provides a unified picture of the evolution of magnetic excitations in various cuprate families, including "hour-glass" and "wine-glass" dispersions and an emergent static incommensurate order. We propose the Lifshitz spin liquid "fingerprint" sum rule, and show that the…
Evidence of a short-range incommensurate $d$-wave charge order from a fermionic two-loop renormalization group calculation of a 2D model with hot spots
Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
利用超流密度和宽带准粒子电导率的高分辨测量,研究了欠掺杂YBCO中节状准粒子的低能激发谱。穿透深度的测量温度低至0.05 K。微波电导率是从0.1到20 GHz测量的,是零能量准粒子的直接探针。的数据进行了比较与预测的一些理论方案,竞争或以其他方式修改纯d波超导性,特别是相称和不相称的自旋和电荷密度波; d + i s和d + i d超导性;循环电流相;和BCS-BEC交叉。我们的结论是,在存在少量强散射无序的情况下,数据与纯d波态一致,并且能够完全排除大多数候选竞争态,或者排除到由无序的能量尺度设置的水平,~ 4 K。然而,相称的自旋和电荷密度顺序,预计不会改变节点的频谱,因此不能排除。
We study the incommensurate charge ordered states in the $\mathit{t-t^{\prime}-J}$ model using the Gutzwiller mean field theory on large systems. In particular, we explore the properties of incommensurate charge modulated states referred to as nodal pair density waves (nPDW) in the literature. nPDW states intertwine site and bond charge order with modulated $d$-wave pair order, and are characterized by a nonzero amplitude of uniform pairing; they also manifest a dominant intra-unit cell $d$-density wave form factor. To compare with a recent scanning tunneling microscopy (STM) study [Hamidian \…
Experiments carried over the last years on the underdoped cuprates have revealed a variety of symmetry-breaking phenomena in the pseudogap state. Charge-density waves, breaking of $C_{4}$ rotational symmetry as well as time-reversal symmetry breaking have all been observed in several cuprate families. In this regard, theoretical models where multiple non-superconducting orders emerge are of particular interest. We consider the recently introduced (Phys. Rev. B 93, 085131 (2016)) spin-fermion model with overlapping 'hot spots' on the Fermi surface. Focusing on the particle-hole instabilities we…
Short-range cluster spin glass near optimal superconductivity in BaFe$_{2-x}$Ni$_{x}$As$_{2}$
当电子被掺杂到铁的反铁磁(AF)母体化合物中时,铁的磷属元素化物会出现高温超导性。除了诱导超导电性,电子掺杂也改变了静态公度AF秩序在未掺杂的母体化合物到短程非公度AF秩序附近的最佳超导电性。本文用中子散射证明BaFe $_{2-x}$ Ni $_{x}$ As $_{2}$中的无公度AF序不是由嵌套费米面中的巡游电子引起的自旋密度波,而是与超导相基质中的团簇自旋玻璃相一致.因此,最佳的超导电性铁pnictides共存,并与介观分离的簇自旋玻璃相竞争,非常不同的均匀共存的AF和超导相在欠掺杂制度。