We solve for the elementary excitation in infinite quasi-1D quantum lattices by extending the recently developed infinite quasi-1D entanglement perturbation theory. The wave function of an excited state is variationally determined by optimizing superposition of cluster operation, each of which is composed of simultaneous on-site operation inside a block of lattice sites, on the ground state in a form of plane wave. The excitation energy with respect to the wave number gives the spectra for an elementary excitation. Our method is artificial broadening free and is adaptive for various quasi-particle pictures. Using the triplet spectrum, the application to $\infty$-by-$N$ antiferromagnetic spin-$\frac{1}{2}$ ladders for $N=2, 4, 6, 8$, and $10$ confirms a previous report that there is a quantum dimensional transition, namely, the lattice transits from quasi-1D to 2D at a finite critical value $N_c=10$. The massless triplet dispersion at $\left( π, π\right)$ sees a vanishing gap. Our results detect the anomaly at $\left(π,0\right)$ in the triplet spectrum, agreeing well with the inelastic neutron scattering measurement of a macroscopic sample. Surprisingly, our results also reveal a gapless and massive 1D singlet dispersion channel that is much lower than the triplet excitation. We note, however, the dimensional transition is determined by the massless triplet dispersion.
Bose Metals and Insulators on Multi-Leg Ladders with Ring Exchange
我们建立了令人信服的证据，证明存在新的准一维后代的d波玻色液体（DBL），一个异国情调的二维量子相的未凝聚巡回玻色子的特点是表面的无隙激发在动量空间[O. I. Motrunich和M. P. A. Fisher，Phys. Rev. B { \bf 75}，235116（2007）]。特别是，出于强耦合分析的规范理论的DBL，我们研究了一个模型的硬核玻色子移动的$N$腿方梯与令人沮丧的四个网站环交换。在这里，我们专注于四腿和三腿系统，我们已经确定了两个新的阶段：一个可压缩的无间隙玻色金属的四腿梯子和不可压缩的无间隙莫特绝缘体的三腿梯子。前者是沿阶梯传导，有五个无间隙模式，比腿的数量多一个。这代表着在建立DBL的二维潜在稳定性方面迈出了重要的一步。后者，另一方面，是一个基本上准一维的阶段，是绝缘沿阶梯，但有两个无隙模式和无公度的幂律横向密度-密度相关。在这两种情况下，我们都可以使用由两个不同的斯莱特行列式的乘积组成的从粒子激发的变分波函数来理解相位的性质，其性质与模型哈密顿量的密度矩阵重整化群解相比令人印象深刻。稳定性参数有利于两个量子阶段访问的普遍低能物理与玻色化分析适当的准一维规范理论。我们将简要讨论这些发现与高温超导体、冷原子气体和受抑量子磁体的潜在相关性。
Singlet quantum phases and magnetization of the frustrated spin-1/2 ladder with ferromagnetic (F) exchange in legs and alternating F-AF exchange in rungs
We study theoretically the quantum phase transition from a metal to a Wigner-Mott insulator at fractional commensurate filling on a two-leg ladder. We show that a continuous transition out of a symmetry-preserving Luttinger liquid metal is possible where the onset of insulating behavior is accompanied by the breaking of the lattice translation symmetry. At fillings $ν= 1/m$ per spin per unit cell, we find that the spin degrees of freedom also acquire a gap at the Wigner-Mott transition for odd integer $m$. In contrast for even integer $m$, the spin sector remains gapless and the resulting insu…
We study a generalized quantum spin ladder with staggered long range interactions that decay as a power-law with exponent $α$. Using large scale quantum Monte Carlo (QMC) and the density matrix renormalization group (DMRG) simulations, we show that this model undergoes a transition from a rung-dimer phase characterized by a non-local string order parameter, to a symmetry broken Néel phase. We find evidence that the transition is second order.In the magnetically ordered phase, the spectrum exhibits gapless modes, while excitations in the gapped phase are well described in terms of triplons -- b…
Using Quantum Monte Carlo simulations, we study the spin-1/2 Heisenberg model on a two-dimensional lattice formed by coupling diagonal ladders. The model hosts an antiferromagnetic Néel phase, a rung singlet product phase, and a topological none trivial Haldane phase, separated by two quantum phase transitions. We show that the two quantum critical points are all in the three-dimensional O(3) universality class. The properties of the two gapped phases, including the finite-size behavior of the string orders in the Haldane phase, are studied. We show that the surface formed by the ladders ends …
We study a generalized quantum spin ladder with staggered long range interactions that decay as a power-law with exponent $α$. Using large scale quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG) simulations, we show that this model undergoes a transition from a rung-dimer phase characterized by a non-local string order parameter, to a symmetry broken Néel phase. We find evidence that the transition is second order. In the magnetically ordered phase, the spectrum exhibits gapless modes, while excitations in the gapped phase are well described in terms of triplons -- boun…
We report the numerical discovery of a pair-density-wave (PDW) superconductor from doping either (i) a spin-one Haldane chain or (ii) a two-leg ladder in the rung singlet phase in which the doped charges occupy a single leg. We model these systems using a generalized Kondo model. The itinerant electrons are correlated and described by the $t-J$ model, and are further coupled to a spin $1/2$ Heisenberg model through the Kondo coupling $J_K$. When the density of electrons $x$ is one, the Mott insulator is in a Haldane phase or in a rung singlet phase depending on whether $J_K$ is negative or pos…
Doped Spin Ladder: Zhang-Rice Singlets or Rung-centred Holes?
我们建立了一个单掺杂自旋梯的电荷转移模型，该模型与Sr $_{3}$ Ca $_{11}$ Cu $_{24}$ O $_{41}$中耦合自旋梯的本征掺杂平面有关。假设存在的实验观察到的电荷秩序在系统中，我们解决了模型使用Hartree-Fock近似。我们的研究结果表明，与最近的X射线吸收测量结果一致，相对于其他配置的掺杂空穴的张-赖斯单态的深刻的稳定性。
Evidence for Dimer Crystal Melting in the Frustrated Spin-Ladder BiCu2PO6
在自旋梯化合物BiCu $_2$ PO $_6$中存在决定性的自旋激发动力学，我们使用非弹性光散射对其进行分类和表征。在（$aa$）、（$bb$）和（$cc$）光散射偏振中，我们观察到了从36 cm $^{-1}$到700 cm $^{-1}$的低能单重态和宽的三重态连续谱。虽然孤立的自旋梯物理可以粗略地解释在高能量下观察到的激发，但需要考虑挫折和梯间相互作用，以充分描述低能量和中等能量下的光谱分布和散射选择规则。更重要的是，在24 cm $^{-1}$处的梯间单重态束缚模式，位于连续区下方，在梯间（$ab$）偏振中显示出其最大的散射强度。与此相反，在62 cm $^{-1}$和108 cm $^{-1}$的能量可比的连续的两个梯子内的束缚态被观察到沿腿（$bb$）和横档（$cc$）的光偏振。我们属性丰富的单重态束缚模式的光谱熔化的二聚体晶体。我们的研究提供了证据Z $_2$量子相变从二聚体到共振价键状态驱动的单线态波动。
In frustrated spin ladders the interplay of frustration and correlations leads to the familiar Haldane (H) and rung-singlet (RS) phases. The nature of the transition between these two phases is still under debate. In this paper we tackle this issue using tools of quantum information theory. We consider frustrated mixed-spin-(1, 1/2) ladders with antiferromagnetic leg, rung and diagonal couplings, and calculate various quantities, such as the entanglement entropy (EE), the Schmidt gap, and the level degeneracy of the entanglement spectrum (ES). We use two numerical techniques, the infinite time…
The Effect of FM Inter-ladder coupling in spin-1/2 AFM two-Leg Ladders in the presence of a magnetic field: Quantum Monte Carlo Study
利用随机级数展开量子蒙特卡罗方法研究了自旋为1/2的具有反铁磁（AFM）腿和横档相互作用的两腿梯中的梯间铁磁（FM）耦合效应。我们比较了Sr $_{14-x}$ Ca $_{x}$ Cu $_{24}$ O $_{41}$ Cuprate的实验测量结果，它是具有FM梯间相互作用的自旋1/2原子力显微镜双腿梯的候选者。在很低的温度下观察到磁化率的显著渐近行为。在没有磁场的情况下，单个自旋为1/2的两腿梯的热力学行为与耦合到$-0.5J_{leg}$相互作用的热力学行为相似。但是，在低磁场下，FM耦合的双腿梯结构的$J_{in}=-0.2 J_{leg}$中的带隙相并不明显，表明梯间FM相互作用可以在零温下诱导出新的量子有序无带隙相。
