The charge transport in the copper-oxygen chain/ladder layers of (La,Y)y(Sr,Ca)14-yCu24O41 is investigated along two crystallographic directions in the temperature range from 50 K to 700 K and for doping levels from y ~= 6 (number of holes nh < 1) to y = 0 (number of holes nh = 6). A crossover from a one-dimensional hopping transport along the chains for y >= 3 to a quasi-two-dimensional charge conduction in the ladder planes for y <~ 2 is observed. This is attributed to a partial hole transfer from chains to ladders when the hole doping exceeds nh ~= 4 and approaches fully doped value n_h = 6. For y <~ 2 a weak dielectric relaxation at radio-frequencies and a microwave mode are detected, which might be recognized as signatures of a charge-density wave phase developed at short length scales in the ladders planes.
Electronic States and Excitation Spectra of Copper Oxides with Ladder and/or Chain
最近报道了具有梯形和共边链的铜氧化物（Sr，Ca）$_{14}$ Cu $_{24}$ O $_{41}$在压力下的超导电性。为了更好地理解超导机制，弄清自掺杂空穴的分布是至关重要的。通过离子模型和精确对角化方法对样品的电导率进行分析，证实了Ca取代Sr后，自掺杂空穴从链状结构转移到了梯状结构。我们还研究了各种铜氧化物中共边链的电子态，并导出了有效哈密顿量。讨论了Cu离子间的磁相互作用和Zhang-Rice单重态的跳跃能与Cu-O-Cu键角的关系。
Role of oxygen-oxygen hopping in the three-band copper-oxide model: quasiparticle weight, metal insulator and magnetic phase boundaries, gap values and optical conductivity
Unconventional Transition from Metallic to Insulating Resistivity in the Spin-ladder Compound (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$
自旋梯化合物是高温超导体有趣的类似物，因为它们含有由铜和氧原子组成的正方形阵列的近一维“梯”层。增加梯子中的腿的数量提供了一种逐步接近二维铜-氧平面的方法，该结构被认为是高温超导性的关键。短程自旋相关的阶梯已被预测，导致形成的空穴对有利于超导性，一旦足够的空穴被引入到阶梯上的掺杂。事实上，在高压下，在两腿梯形化合物（Sr，Ca）$_{14}$ Cu $_{24}$ O $_{41}$中已经发现了超导性。在这里，我们表明，在非超导状态下的（Sr，Ca）$_{14}$ Cu $_{24}$ O $_{41}$共享三个不同的制度，在共同的高温超导体，包括一个无法解释的绝缘行为在低温下的电阻率增加的温度的对数。这些观察结果表明，对数发散来自一个新的本地化机制共同的梯形化合物和高温超导体，这可能是由于近一维的电荷输运在自旋间隙的存在。
Correlated-electron theories of superconductivity in layered cuprates often start from the premise of a gapped spin-liquid phase proximate to the superconducting state. This assumption is justified based on analytical and numerical demonstrations of a superconducting Luther-Emery phase in the doped 2-leg one-band Hubbard ladder, and the perceived analogy between coupled ladders and the two dimensional CuO2 layer. We demonstrate from accurate density matrix renormalization group studies the absence of the superconducting Luther-Emery phase in the doped 2-leg three-band ladder consisting of both…
Magneto-elastic coupling between copper spin configurations and oxygen octahedra in La(2-x)Sr(x)CuO(4). Untwinning, Raman (phonon) spectrum, and neutron response
Experiments on Ladders Reveal a Complex Interplay between a Spin-Gapped Normal State and Superconductivity
近年来，梯型材料的研究已发展成为强关联电子大背景下的一个成熟的研究领域。这一努力是由理论和实验之间不寻常的交叉施肥引发的。在本文中，主要的实验结果中所获得的背景下的梯子从理论家的角度进行了审查。重点讨论了二维高$\rm T_c$铜酸盐和两个梯形化合物之间的许多相似之处，包括Sr $_{14-x}$ Ca $_x$ Cu $_{24}$ O $_{41}$（14-24-41），它在高压下具有超导相和小的空穴密度。这些相似之处的例子包括制度的线性电阻率与温度的金属梯和正常状态的自旋间隙或赝间隙的特点。在这方面的一些有争议的结果进行了讨论。值得注意的是，梯形14-24-41是第一种具有非正方形晶格层状排列的超导氧化铜材料，当然，从对这种化合物的仔细分析中可以学到很多东西。在这一领域的主要理论发展的简短总结也包括在内，以及一个简短的描述的性质的非铜氧化物阶梯。文中介绍了作者对可能的实验提出的建议。总体而言，可以得出结论，在梯子上进行的巨大的实验努力已经揭示了相当具有挑战性和有趣的物理，增加了过渡金属氧化物中的电子的丰富行为，并有助于理解二维铜酸盐。然而，仍然需要进行大量的工作，以充分了解这些材料中电荷和自旋自由度之间的相互作用。
Nuclear Spin Relaxation in Hole Doped Two-Leg Ladders
本文测量了空穴掺杂的双柱梯形化合物Sr $_{14-x}$ Ca $_{x}$ Cu $_{24}$ O $_{41}$和未掺杂的母体材料La $_6$ Ca $_8$ Cu $_{24}$ O $_{41}$的核自旋-晶格弛豫速率（$1/T_{1}$）。在铜和两个不同的氧站点的$1/T_{1}$的比较显示，低频自旋波动的主要光谱权重位于附近的$q \sim (π, π)$的温度和掺杂范围的调查。在重掺杂$x$ =12样品中，两个氧位点的$1/T_1$的温度依赖性的显著差异揭示了两个腿之间的单线态相关性的降低，而不是随着温度的升高而沿着腿方向增长的反铁磁相关性。这种行为很可能是由束缚空穴对的解离引起的。
We follow the evolution of Copper and Oxygen two-hole excitations, in optimally doped (Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x} $)Cu$_{3}$O$_{y}$ for $x=0.1$ and $x=0.4$. The spectra have contributions from band states as well as a localized multiplet structure. From their identification, we determine the intrashell Coulomb interaction $U$ for Oxygen and Copper sites. These results allow us to estimate the atomic superexchange coupling $J$ suggesting a positive correlation between the maximal superconducting critical temperature $T_\text{C}^{max}$ and $J$.
Spin-spin correlations of the spin-ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ measured by magnetostriction and comparison to Quantum Monte Carlo results
详细分析了自旋梯型化合物哌啶溴化铜（C $_5$ H $_{12}$ N）$_2$ CuBr $_4$的磁致伸缩和热膨胀。我们发现完美的协议之间的实验和理论的两个腿的自旋阶梯哈密顿超过十年的温度和在很宽的磁场范围。将不同晶向的磁致伸缩与两个静态自旋-自旋关联函数联系起来，用量子蒙特卡罗方法计算了（C $_5$ H $_{12}$ N）$_2$ CuBr $_4$的磁弹性耦合.我们特别关注两个临界磁场$H_{c1}$和$H_{c2}$附近的量子临界行为，其特征在于源于临界自旋系统的低维性的强奇异性。扩展我们在Lorenz等人[Phys. Rev. Lett.，100，067208（2008）]，我们明确表明，上临界场$H_{c2}$附近的热膨胀是定量描述的一维，非相对论性费米子的无参数理论。我们还指出弹性模量存在奇异量子临界修正。这种校正与磁化率$χ$成比例，其在临界场处发散为$χ\sim 1/\sqrt{T}$，从而导致晶体的强烈软化。
A major open topic in cuprates is the interplay between the lattice and electronic dynamics and the importance of their coupling to the mechanism of high-temperature superconductivity (HTSC). As evidenced by Extended X-ray Absorption Fine Structure experiments (EXAFS), anharmonic structural effects are correlated with the charge dynamics and the transition to a superconducting phase in different HTSC compounds. Here we describe how structural anharmonic effects can be coupled to electronic and lattice dynamics in cuprate systems by performing the exact diagonalization of a prototype anharmonic…
One of the deepest questions in condensed matter physics concerns what other phases compete with superconductivity in high-transition-temperature (high-Tc) superconductors. One candidate is the "stripe" phase, in which the carriers (holes) condense into rivers of charge separating regions of antiferromagnetism. A related but lesser known system is the "spin ladder", which consists of two coupled chains of magnetic ions forming an array of rungs. A doped ladder can be thought of as a high-Tc material with lower dimensionality, and has been predicted to exhibit both superconductivity and an insu…
