Theoretical study of one-dimensional quantum spin sustems : q in which two kinds of spins are arranged alternatively

我们对量子混合自旋-1/2-1/2-1-1链描述的汉密尔顿H = 1/2/4（/）l=1/D3进行了分析和计算。（JイイD21イイD2·SイD4 ~ EイD24l-3イD2·SイD4 ~ EイD24l-2イイD2 + JイD22イD4 ~ EイD24l-2イD2·SイD4 ~ EイD24l-1イD2 + JイD23イD4 ~ E D24l-1イD4 ~ E D24l-1イD2·SイD4→ EイD4イイD24lイエD2 + JイD22イエD4→ EイD24lイエD2·SイD4→ EイD24l+1イエD2），两个S = 1/2旋转（SイD4 ￣ EイD4 ￣ EイD24l-3 EイD2 and S D 4 ￣ E D 4 ￣ E D 24l-2 E D 2） and two S = 1 spins （SイD4 ￣ E D 4 ￣ E D24l-）1型D2 and型D4→型D4型D24 l型D2 are arrayed alternatively.In several limiting cases of J型D21型D2， J型D22型D2， and J型D23型D2 we have applied the Wigner-Eckart theorem and carried out a perturbation calculation to examine the beManagement ors， in these cases，在那些无障碍的线条中，能量差距消失的地方。根据这些结果的指导，我们已经完成了一个密度矩阵再生均衡-组计算，以确定T上的地面状态相位图。 ... More he JイイD21イエD2 versus JイD22イエD2 plane with JイD23イエD2 = 1. 0。从单口三口能量差距的无间隙点，五条边界线已经确定，将相位图表分成六个区域。在三个地区，地面状态与Haldane相位字符出现，但在保留的三个地区，这些区域与二聚体字符出现。我们还介绍了各阶段的特征，讨论了每个阶段的地面状态如何表现在Valence-Bond-Solid（VBS）框架中。由于使用矩阵-产品波功能，我们已经分类了VBS图片，并解释了与VBS图片的对称性术语的地面状态相位图。我们研究了离地面状态最近的两个自旋相关函数和一种字符串顺序参数，我们已经确认了字符化的有效性。Furthermore，我们已经排除了量子蒙特卡罗计算，该计算将全球翻转沿Trotter方向进行核算，以抵消特定热量和磁性可行性的温度依赖性。In particular， we have found that the specific heat per unit cell versus temperature curve for JイD22イイD2 = 5. 0 with JイD21イD2 = JイD23イD2 = 1. 0 has a double peak。Less（低）

We have investigated both analytically and numerically the ground-state and thermodynamic properties of the quantum mixed spin-1/2-1/2-1-1 chain described by the Hamiltonian H = ΣィイD31N/4(/)l=1ィエD3(JィイD21ィエD2・SィイD4→ィエD4ィイD24l-3ィエD2・sィイD4→ィエD4ィイD24l-2ィエD2 + JィイD22ィエD2 sィイD4→ィエD4ィイD24l-2ィエD2・SィイD4→ィエD4ィイD24l-1ィエD2 + JィイD23ィエD2 SィイD4→ィエD4ィイD24l-1ィエD2・SィイD4→ィエD4ィイD24lィエD2 + JィイD22ィエD2 SィイD4→ィエD4ィイD24lィエD2・sィイD4→ィエD4ィイD24l+1ィエD2), where two S = 1/2 spins (sィイD4→ィエD4ィイD24l-3ィエD2 and sィイD4→ィエD4ィイD24l-2ィエD2) and two S = 1 spins (SィイD4→ィエD4ィイD24l-1ィエD2 and ィイD4→ィエD4ィイD24lィエD2 are arrayed alternatively.In several limiting cases of JィイD21ィエD2, JィイD22ィエD2, and JィイD23ィエD2 we have applied the Wigner-Eckart theorem and carried out a perturbation calculation to examine the behaviors, in these cases, of the massless lines where the energy gap vanishes. Guided by these results, we have performed a density-matrix renormalization-group calculation to determine in detail the ground-state phase diagram on t … More he JィイD21ィエD2 versus JィイD22ィエD2 plane with JィイD23ィエD2 = 1.0. From the gapless points of the singlet-triplet energy gap, five boundary lines have been determined, which divide the phase diagram into six regions. In three regions the ground states with the Haldane-phase character appear, while in the remaining three regions those with the dimer character appear. We have also presented a characterization of the phases concerning how the ground state in each phase is represented in the framework of the valence-bond-solid (VBS) picture. Making use of the matrix-product wave function, we have classified the VBS pictures and interpreted the ground-state phase diagram in terms of symmetries schematically related to the VBS pictures. We have investigated the ground-state nearest-neighboring two-spin correlation functions and a kind of string order parameters, by which we have confirmed the validity of the characterization.Furthermore, we have carried out a quantum Monte Carlo calculation which takes the global flips along the Trotter direction into account to elucidate the temperature dependences of the specific heat and the magnetic susceptibility. In particular, we have found that the specific heat per unit cell versus temperature curve for JィイD22ィエD2 = 5.0 with JィイD21ィエD2 = JィイD23ィエD2 = 1.0 has a double peak. Less