报道了高转变温度（Tc）铜酸盐超导体Bi{2+x}Sr{2-x} CaCu 2 O {8+δ}和YBa 2 Cu 3 O 6. 57的低温μ子自旋弛豫（muSR）测量结果，旨在探测四种不同铜酸盐家族赝能隙相中通过自旋极化中子散射观察到的神秘的单胞内（IUC）磁序。由于缺乏局部磁探针方法的确认，提出了这样一种可能性：磁序波动得足够慢，在中子散射的时间尺度上看起来是静态的，但波动得太快，不会影响$μ$ SR或核磁共振（NMR）信号。IUC磁序与铜氧化物的理论模型相联系，该模型预测了电子-电流回路序的长程有序相，其终止于量子临界点（QCP）。我们的研究表明，将温度降低到T ~ 25 mK，并远远低于所谓的QCP，并不会导致足够的IUC磁序的波动放缓，成为可检测的时间尺度上的μ SR。我们的测量对这种未识别的磁序的波动率有很小的限制。
英文摘要：
We report low temperature muon spin relaxation (muSR) measurements of the high-transition-temperature (Tc) cuprate superconductors Bi{2+x}Sr{2-x}CaCu2O{8+δ} and YBa2Cu3O6.57, aimed at detecting the mysterious intra-unit cell (IUC) magnetic order that has been observed by spin polarized neutron scattering in the pseudogap phase of four different cuprate families. A lack of confirmation by local magnetic probe methods has raised the possibility that the magnetic order fluctuates slowly enough to appear static on the time scale of neutron scattering, but too fast to affect $μ$SR or nuclear magnetic resonance (NMR) signals. The IUC magnetic order has been linked to a theoretical model for the cuprates, which predicts a long-range ordered phase of electron-current loop order that terminates at a quantum crictical point (QCP). Our study suggests that lowering the temperature to T ~ 25 mK and moving far below the purported QCP does not cause enough of a slowing down of fluctuations for the IUC magnetic order to become detectable on the time scale of muSR. Our measurements place narrow limits on the fluctuation rate of this unidentified magnetic order.
Ab initio Understanding of the Pseudogap in Cuprate High Temperature Superconductors via the Fluctuating Bond Model
理解赝能隙的起源是阐明铜氧化物超导体中的配对机制的重要一步。最近有强有力的实验证据表明，C4对称性破缺发生在赝能隙的形成。这种形式的对称性破缺是由波动键模型（FBM）预测的，波动键模型是一种基于电子与平面氧振子振幅平方的强局部耦合的经验模型。在本文中，我们从一个新的方向，从{ \it ab initio}分子动力学模拟开始的FBM理论。模拟结果表明，掺杂依赖的不稳定性的面内氧对位移的Cu-O-Cu键轴。根据这些结果和微扰理论，我们导出了涨落键模型的一个改进的定量形式。FBM的平均场解导致氧振动振幅的C4对称性破缺，以及电子光谱中的d型赝能隙，这些特征与最近的实验数据有关。从平均场论推导出的赝能隙的相图，其掺杂和温度依赖性，包括相边界T $^*$，符合实验数据。我们扩展的理论，包括长程库仑相互作用的FBM相互作用的基础上。当长程库仑相互作用包括在FBM中，电荷通道中的CDW不稳定性的预测，这解释了纳米级，而不是空间均匀的，行为的C4的库仑断裂。考虑到CDW，与理论上的k依赖性的赝隙，使费米表面弧现象得到理解。
We study the physical property of pair density wave (PDW) and fluctuating PDW, and use it to build an effective theory of the strongly interacting pseudogap phase in cuprate high temperature superconductors. In Chapter2, we study how Fulde-Ferrell state, the simplest form of PDW, responds to incident light. The collective motion of the condensate plays a key role; gauge invariance guides us to the correct result. From Chapter 3 to Chapter 7, we construct a pseudogap metallic state by considering quantum fluctuating PDW. We analyze a recent scanning tunneling microscope (STM) discovery of perio…
On the dilemma between percolation processes and fluctuating pairs as the origin of the enhanced conductivity above the superconducting transition in cuprates
Intra unit cell (IUC) magnetic order observed by polarized neutron diffraction (PND) is one of the hallmarks of the pseudogap state of high-temperature copper oxide superconductors. This experimental observation, usually interpreted as a result of loop currents, has been recently challenged based on lower statistics data. We here address the crucial issue of polarization inhomogeneities in the neutron beams showing that the original data had a much better reproducibilty. Within these technical limitations, we here propose a self-consistent analysis that potentially solves the controversy. We s…
Fluctuating orders and quenched randomness in the cuprates
本文研究了准二维经典Landau-Ginzburg-Wilson有效场论在淬火无序存在下的超导有序和无公度电荷密度波的相互作用.这种无序排除了长程电荷密度波序，但不排除超导或超导有序。我们选择了三组有代表性的输入参数和计算相应的电荷密度波结构因子使用大$N$技术和经典的蒙特卡罗模拟。向列性和超导性在低温下共存的地方，电荷密度波结构因子的峰高作为温度升高的函数单调下降，这与在YBa $_2$ Cu $_3$ O $_{6+x}$的X射线实验中所看到的不同。相反，在热演化的电荷密度波的结构因子定性与实验一致，计算到一个循环的顺序，是短于电荷密度波的相关长度。
Electronic Liquid Crystal Physics of Underdoped Cuprates
最近对对称性破缺的观察，部分地揭开了赝能隙相的神秘面纱。在这里，我们审查的证据，长程内的单位细胞（IUC）的顺序和它的意想不到的强耦合的相位的波动条纹的赝能隙状态的欠掺杂的Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$。特别是，我们专注于分析技术，揭示了这一证据，在扫描隧道光谱数据中，提取的IUC的顺序序参量的定义，和IUC的顺序和先前报道的共存的波动条纹之间的耦合的唯象理论。我们还提出了一个微观机制的IUC的有序驱动的现场和近邻排斥。最后，我们讨论这些结果的背景下，开放的问题。
The thermal fluctuations contribution to magnetization and magneto-conductivity of type II layered superconductor is calculated in the framework of Lawrence-Doniach model. For numerous high temperature cuprate superconductors, it was discovered that the magnetization dependence on temperature in wide range of fields exhibits an intersection point at a temperature slightly below $T_{c}$. We notice a similar intersection point of the magneto-conductivity curves at the approximate same temperature. The phenomenon is explained by strong (non-gaussian) thermal fluctuations with interactions treated…
Recent advances in momentum-resolved electron energy-loss spectroscopy (MEELS) and resonant inelastic X-ray scattering (RIXS) now allow one to access the charge response function with unprecedented versatility and accuracy. This allows for the study of excitations which were inaccessible recently, such as low-energy and finite momentum collective modes. The SU(2) theory of the cuprates is based on a composite order parameter with SU(2) symmetry fluctuating between superconductivity and charge order. The phase where it fluctuates is a candidate for the pseudogap phase of the cuprates. This theo…
The intra-unit-cell nematic phase is studied within the three-band Emery model of the cuprates with the use of the approach based on the diagrammatic expansion of the Gutzwiller wave function (DE-GWF). According to our analysis the spontaneous $C_4$ symmetry breaking of the electronic wave function, leading to the nematic behavior, can appear due to electron correlations induced mainly by the onsite Coulomb repulsion, even in the absence of the corresponding intersite oxygen-oxygen repulsion term. The latter has been considered as the triggering factor of the nematic state formation in a numbe…
Temperature dependencies of excess conductivity, Sigma', have been studied in detail for three FeSe_{0.94} textured polycrystalline samples prepared by partial melting and solid state reaction. It was revealed that both Sigma' and its temperature dependence are extremely sensitive to the method of sample preparation. Then, it was shown that in the range from the superconducting transition temperature Tc ~ 9 K up to the characteristic temperature T_01 ~ 19 K, Sigma'(T) obeys the classical fluctuation theories of Aslamazov-Larkin (AL) and Hikami-Larkin (Maki-Thompson (MT) term) pointing to the e…
Intra pseudogap- and superconductivity-pair spin and charge fluctuations and underdome metal-insulator (fermion-boson)-crossover phenomena as keystones of cuprate physics
On the "spin-freezing" mechanism in underdoped superconducting cuprates
这封信涉及的自旋冻结过程中观察到的核磁共振-NQR弛豫或μ子自旋旋转欠掺杂铜酸盐超导体。这种现象，有时被称为反铁磁和超导序参数的共存，通常被认为是由随机分布的磁矩与电荷不均匀性（可能是条纹），这表现出他们的波动在T $_c$以下冷却减慢。相反，我们描述的实验结果，由于波动，涡旋-反涡旋，轨道电流状态共存的d波超导状态。一个直接的解释的实验结果，在欠掺杂的Y $_{1-x}$ Ca $_x$ Ba $_2$ Cu $_3$ O $_{6.1}$和La $_{2-x}$ Sr $%_x$ CuO $_4$，从而给出了冻结的轨道电流波动。
Identifying quantum critical points (QCPs) and their associated fluctuations may hold the key to unraveling the unusual electronic phenomena observed in cuprate superconductors. Recently, signatures of quantum fluctuations associated with charge order (CO) have been inferred from the anomalous enhancement of CO excitations that accompany the reduction of the CO order parameter in the superconducting state. To gain more insight about the interplay between CO and superconductivity, here we investigate the doping dependence of this phenomenon throughout the Bi-2212 cuprate phase diagram using res…
We first present detailed measurements of the rounding behavior around the superconducting transition temperature, $T_c$, of the in-plane electrical conductivity, magnetoconductivity and magnetization, including the low and moderate magnetic field regimes, in a high-quality single crystal and a thin film of the prototypical optimally-doped YBa$_2$Cu$_3$O$_{7-δ}$ (OPT Y-123), in which the inhomogeneity effects are minimized. Then, it is presented a comparison of these experimental data with the phenomenological Ginzburg-Landau (GL) approach that takes into account the unavoidable contribution o…
