Spin dynamics of quantum spin-ladders and chains
Spin dynamics of quantum spin-ladders and chains
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量子自旋梯和链的自旋动力学
DOI：
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发表时间：
2007
期刊：
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通讯作者：
S. Notbohm
中科院分区：
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作者：
S. Notbohm
本文描述了自旋链和阶梯中磁激发的中子散射测量。第一部分讨论了由边共享链和自旋梯组成的氧化铜家族Sr 14Cu24O41的实验研究。La4Sr10Cu24O41的研究包括一个微空穴掺杂链和一个未掺杂的阶梯结构，其中链条可以通过铁磁最近邻和反铁磁次近邻耦合来建模。这种效应在色散关系的间隙中很明显，可以用符合色散比例的电荷密度波来描述。通过对未掺杂阶梯的研究，建立了交换常数，包括由双磁振子连续统和S = 1束缚模式抑制引起的循环交换流形。轨道的考虑为交换提供了一个解释，包括不同尺寸的梯级和腿耦合。Ca2.5Sr11.5Cu24O41中掺杂阶梯的激发谱可以直接与未掺杂阶梯进行比较，由高能量模式和亚间隙散射组成的差异可以通过由自由电子模型计算的阶梯的电荷谱成功地模拟出来。论文的第二部分研究了交替链材料Cu(NO3)2·2.5D2O，并首次建立了间隙的1 -磁振子色散、2 -磁振子非连续体和theS =1束缚模式。施加磁场驱动系统通过两个关键的场跃迁，即磁振子凝聚到基态和饱和。超过饱和的模态可以用自旋波理论来描述，在第一临界场处的激励遵循Luttinger Liquid行为。此外，还研究了具有不同性质但包含强相关系统特征的激励的温度效应。为了展望包括温度和场在内的测量，提供了必要的进一步理论描述。
This thesis describes the neutron scattering measurements of magnetic excitations in spin-chains and ladders. The first part discusses an experim ental investigation of the copper oxide family Sr 14Cu24O41 composed of edge-sharing chains and spin-ladders. The study of La4Sr10Cu24O41 comprises a slightly hole-doped chain and an undoped ladder structure where the chain can be modeled by a ferromag netic nearest and an antiferromagnetic next-nearest neighbor coupling. The ho l effects are apparent in gaps in the dispersion relation and can be described by a charge-d ensity wave agreeing with the commensuration of the dispersion. Investigating the un doped ladder establishes the exchange constants including a cyclic exchange manifes ted by the two-magnon continuum and the suppression of the S = 1 bound mode. An orbital consideration provides an explanation for the exchanges including the di fferent sizes of rung and leg coupling. The excitation spectrum of the doped ladder in Ca2.5Sr11.5Cu24O41 can be described by a direct comparison with the undoped ladder and the ifferences consisting of a higher energy mode and subgap scattering can be successf ully modeled by the charge spectrum of the ladder calculated from the free elect ron model. The second part of the thesis investigates the alternating chain mater ial Cu(NO3)2 · 2.5D2O and establishes the gapped one-magnon dispersion, the two-mag non continuum and for the first time theS =1 bound mode. Applying magnetic field drives the system throu gh two critical field transitions, condensation of magnons into th e ground state and saturation. The modes beyond saturation can be modeled by spin wave theor y and the excitations i at the first critical field follow Luttinger Liquid behavior. Additionally investigated are the temperature e ffects with the excitations being of a di fferent nature but containing the signature of a strong correlated system. For an outlook t he measurements including temperature and field are provided with further theoretical descriptions necessary.