Studies of elemental substitution effect in spin-gap systems by density matrix renormalization group method

密度矩阵重正化群法研究自旋能隙体系中的元素取代效应

基本信息

批准号：
11640363
负责人：
YOKOYAMA Hisatoshi
金额：
$ 1.73万
依托单位：
Tohoku university
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

In connection with the pseudogap and impurity effect in high temperature superconductors, we have investigated chiefly elemental substitution effect in various quasi one-dimensional spin systems which show spin-gap behaviors, by using the density matrix renormalization group and exact diagonalization methods. We consider a one-dimensional spin model with two parameters, next-nearest-neighbor coupling α and bond alternation β. This model can be applied to all the materials of our concern, [1] Haldane systems, [2] bond-alternating ones, [3] spin-Peierls ones and [4] spin ladder ones. A series of calculations has been performed for pure states and ones with impurities. Main results are : (1) According to the gap, spin correlation length ζ and the string order parameter, the whole space spanned by α and β for the pure systems (size L=∞ ) belongs to the so-called Haldane phase except for the two limiting cases of 'spin liquid' : β=1 (no bond alternation) and α=∞ (independent two S=1/2 Heise … More nberg chains). (2) When non-magnetic impurities are doped (L is finite) , not only ζ but the behaviors of spin polarization in the states with <S^e_i>≠0 are distinct between the typical Haldane regime and the one near the spin-liquid lines. For the former, ζ and <S^e_i> (namely magnetic excitation) are independent of L and spin polarization is localized near the chain end (impurity site). Meanwhile, for the latter staggered magnetization spreads over the whole chain and its amplitude abruptly increases with decreasing L.Thus, we see that the material groups [1] and [2] belonging to the formar category preserve the gap properties even for highly doping, whereas for [3] and [4] in the latter category a tiny amount of impurity disrupts the gap and leads to an antiferromagnetic long range order. (3) In this model incommensurate spin correlation had been anticipated and partly known. We have elucidated the phase diagram in the whole α-β space for T=0. Moreover, discordance of the incommensurability between the real and momentum spaces has been discussed in the light of quantum fluctuation.Based on the above results for spin systems, we have progressed our calculation to the electronic ones, especially taking account of the pseudogap and stripe structure for high temperaure superconductors. The study in this line will be succeeded in the project of next term. Less

与高温超导体中的伪gap和杂质效应有关，我们通过使用密度矩阵肾脏重新分配组和精确的对角色方法，在各种准准一维旋转系统中投资了基本的元素替代效应，这些元素替代效应显示出旋转隙行为。我们考虑一个具有两个参数的一维自旋模型，即临界最新的耦合α和键替代β。该模型可以应用于我们关注的所有材料，[1] haldane系统，[2]键 - 偏置的系统，[3]旋转peierls和[4]旋转梯子。为纯状态和具有杂质的状态进行了一系列计算。主要结果是：（1）根据间隙，自旋相关长度ζ和弦顺序参数，纯系统（尺寸l =∞）跨越α和β跨越的整个空间属于所谓的haldane相，除了两个限制案例的“旋转液体”：β= 1（无键替代）和α=∞（无独立的两个s = 1 s = 1 = 1 = 1-2），除了两个限制案例。（2）当非磁性杂质被掺杂（L是有限的）时，不仅是ζ，而且在<s^e_i>≠0状态中自旋极化的行为在典型的haldane状态与旋转液体附近的典型霍尔达内型之间有所不同。对于前者，ζ和<s^e_i>（即磁兴奋）与L无关，并且自旋极化位于链端（杂质位点）附近。 Mean while, for the latter staggered magnetization spreads over the whole chain and its amplifier abruptly increases with decreasing L.Thus, we see that the material groups [1] and [2] belonging to the formar category preserve the gap properties even for highly doping, whereas for [3] and [4] in the latter category a tiny amount of impurity disrupts the gap and leads to an antiferromagnetic long范围顺序。（3）在此模型中，预期并部分知道了自旋相关。我们已经阐明了T = 0的整个α-β空间中的相图。此外，根据量子波动，已经讨论了真实和动量空间之间不可通信的性能。基于上述旋转系统的结果，我们将计算进展到电子量的计算，尤其是考虑到高气温超导节的伪gap和条纹结构。该行中的研究将在下一学期的项目中取得成功。较少的