Underdoped cuprates, manifestations of boson-fermion crossover, `quantum oscillations' and the robust fractional quantum Hall state nu = 2/5
John A. Wilson
备注：
51 pages and 18 figures. Submitted to J.Phys.:Condens. Matter, 30 April 2011. Still awaiting referees' reports! v2 contains many small wording improvements
The quantum oscillation data from a whole variety of underdoped HTSC systems and physical measurements has almost universally been presented in very classical terms following the Lifshitz-Kosevich formulation for Fermi-Landau quasiparticles, quantized into vortices and Landau levels under the high applied magnetic fields. The Fermi surface always emerges as a very small fraction of the large parent Fermi surface detected at higher doping. This then calls for some Fermi surface reconstruction to have occurred, as from a charged density wave, etc.. The paper refutes this reciprocal space approach, and shows that many of the more recent detailed works taking this line are not consistent with the data. The present author developed an alternative real-space interpretation of these matters a couple of years ago. This was in terms of interaction of the vortex array with the stripe array, using a 2D modelling for the latter. This approach has here been revised slightly and copes well with addressing the wide variety of new data. The paper pursues and justifies the BEC/BCS, negative-U based, two-subsystem modelling advocated earlier, along with the strength and geometry of the striping acquired in a strong magnetic field. A wide variety of recent experiments are expounded to produce an overall appreciation of a situation far from being appropriately treated within a Fermi-Landau quasiparticle framework. Indeed it is demonstrated that the universality of the 'QO' observations ensues from the fractional quantum Hall effect. The data all point to FQHE state with filling factor nu = 2/5. This state in its genesis and expression finds a much greater alignment with the BEC/BCS crossover condition and the proximity of the HTSC materials to Mott-Anderson localization than does any model for this highly correlated material appealing to well-metallized Fermi-Landau quasiparticle physics.
Doping-dependent critical Cooper-pair momentum in thin, underdoped cuprate films
我们应用一个最近开发的低场技术感应测量的临界对动量$p_c$在薄，欠掺杂薄膜的Y $_{1-x}$钙$_{x}$钡$_{2}$铜$_{3}$ O $_{7-δ}$和Bi $_{2}$锶$_{2}$钙铜$_{2}$ O $_{8+δ}$反映了广泛的空穴掺杂。我们观察到，$p_c \propto \hbar/ξ$的规模与$T_c$，因此超流体密度$n_s(T\rightarrow0)$在我们的二维铜酸盐薄膜。这种关系是著名的预测与\textit{doping-independent}超导间隙的铜氧化物的通用模型，但尚未观察到的相干长度$ξ$的高场测量由于场诱导现象不包括在理论中。
用低温热输运方法研究了高纯轻掺杂铜酸盐$_{2}$ O $_{3}$单晶的基态.在零磁场和外加磁场下，在超导相边界的两侧测量样品。我们报道了在非超导态中零能离域费米激发的观测结果，这表明欠掺杂铜氧化物的基态是金属态。它的低能谱似乎与d波超导体相似，即波节。在欠掺杂La $_{2-x}$ Sr $_{x}$ CuO $_4$中观察到的绝缘基态归因于该系统中存在的竞争自旋密度波序。
Evidence for a superconducting origin of prominent features of the in-plane infrared response of underdoped cuprates and implications of their persistence above $T_{\mathrm{c}}$
Proposed measurements of the interlayer magnetoresistance of underdoped cuprate superconductors can distinguish closed pockets from open arcs in the Fermi surface
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。
Annealing effects on the normal-state resistive properties of underdoped cuprates
研究了室温退火对欠掺杂YBa $_2$ Cu $_3$ O $_{7-δ}$和HoBa $_2$ Cu $_3$ O $_{7-δ}$单晶正常态和超导态基平面电阻参数的影响。衍生物$dρ(T)/dT$的形式使得可以确定波动电导率的起始温度，并指示不稳定氧的不均匀分布。退火已被揭示为导致缺氧的单调减少，这主要表现为残余电阻的减少、$T_c$的增加和德拜温度的降低。
Field-dependent specific heat of the canonical underdoped cuprate superconductor YBa$_2$Cu$_4$O$_8$
铜酸盐超导体YBa $_2$ Cu $_4$ O $_8$与大多数其他铜酸盐相比，具有稳定的化学计量比，基本上没有缺陷，可以被认为是典型的欠掺杂铜酸盐，显示出明显的赝能隙行为和相关的超导性质的明显减弱。这种铜酸盐的“pseudogap”表现为在费米能级的电子态密度的部分间隙，并在大多数光谱特性中观察到。经过几十年的深入研究，人们普遍认为，赝能隙在特征温度$T^*$附近闭合，类似于平均场，该温度随着空穴浓度$p$的降低而升高。在这里，我们报告了广泛的依赖于场的电子比热研究YBa $_2$ Cu $_4$ O $_8$高达前所未有的400 K，并明确表明，pseudogap永远不会关闭，保持开放至少400 K，其中$T^*$通常被假定为约150 K。我们从核磁共振奈特位移和电子熵表明，威尔逊比是一个弱相互作用的费米子系统的近节态的数值一致。并从与场相关的比热出发，讨论了涨落和杂质散射对热力学性质的影响。
Screening of point charge impurities in highly anisotropic metals: application to $μ^+$ spin relaxation in underdoped cuprates
我们计算屏蔽电荷密度分布由于点电荷，如正μ子（$μ^+$），放置在平面之间的高度各向异性的层状金属。在欠掺杂的空穴铜氧化物中，屏蔽电荷将$μ^+$附近的金属平面晶胞中的电荷密度转换为接近其在绝缘状态下的值。极化中子衍射所观察到的电流环有序状态，然后消失在这样的细胞，也在附近的细胞在一个距离的顺序的内在相关长度的环有序状态。这又强烈地抑制了$μ^+$位置处的回路电流场。我们估计了欠掺杂$_2$ Cu $_3$ O $_{6+x}$和La $_{2-x}$ Sr $_x$ CuO $_4$中的抑制场，发现在前一种情况下与观测到的0.2- 0.3 G场一致，在后一种情况下与观测到的$\sim$ 0.2 G上界一致.这解决了中子衍射和$μ$ SR实验之间的争议。筛选计算也有相关的铜酸盐中的其他电荷杂质的影响，如掺杂剂本身。
Neutron Scattering Evidence for a Periodically-Modulated Superconducting Phase in the Underdoped Cuprate La$_{1.905}$Ba$_{0.095}$CuO$_4$
反铁磁自旋关联在高温超导体中的作用仍然是一个有争议的问题。我们提出的非弹性中子散射证据表明，在La $_{1.905}$ Ba $_{0.095}$ CuO $_4$中，无带隙自旋涨落与超导电性共存。此外，我们还观察到超导关联的出现增强了低能磁谱权重和自旋不变性。我们认为这种共存是通过对波函数的空间调制和反铁磁关联的相互作用而发生的。该提议也与充分欠掺杂的La $_{2-x}$ Sr $_x$ CuO $_4$和YBa $_2$ Cu $_3$ O $_{6+x}$直接相关。
