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The study on a new quantum-spin phase in a quantum ladder system

量子梯系统中新的量子自旋相的研究

基本信息

批准号：
11640355
负责人：
DEGUCHI Hiroyuki
金额：
$ 2.3万
依托单位：
KYUSHU INSTITUTE OF TECHNOLOGY
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

New quantum antiferromagnetic chains, spin-ladder systems, have attracted a lot of theoretical and experimental interest. An even-leg ladder is believed to be a spin-gap system and to have a short-range resonating valence bond (RVB) ground state. The compound Cu_2 (C_5H_<12>N_2)_2Cl_4 (hereafter, CHpC) is a typical two-leg ladder system with exchange interaction for the rungs (J_⊥ /k=13.2K) and for the legs (J _<//>/k=2.4K) of the ladder and a spin-gap energy of Δ/k=l0.5K.Recently, we reported experimental results of a new compound Cu_2(C_5H_<12>N_2)_2Br_4 (hereafter, CHpB) of which crystal structure is isostrucural with CHpC.The results suggest that the compound CHpB is a spin-ladder system with a spin-gap like CHpC.We estimated the exchange interactions J _⊥/k=24.8K, J _<//>/k=3.5K and a spin-gap energy of Δ/k=21.3K.Therefore, the random mixture compound Cu_2(C_5H_<12>N_2)_2 (Cl_<1-x>Br_x)_4 seems to be a ladder system with random antiferromagnetic bonds. The magnetic properties of a … More random mixture compound Cu_2(C_5H_<12>N_2)_2 (Cl_<1-x>Br_x)_4 are rather different from those of the pure systems. Paramagnetic divergence is significantly observed for the susceptibility at low temperatures and the magnetization appears even at low fields. For random systems, the susceptibilities do not follow the Curie law and diverge stronger than the Curie law. The systems with strong randomness are in a random singlet phase or are in a Griffice phase of which susceptibility diverges at low temperatures. The heat capacity of both pure and random systems was measured at low temperatures. In the cases of pure systems, the behavior of heat capacities is of the exponential type T^2exp (-Δ/kT), where Δ is the gap energy for the collective excitation. For random systems, the heat capacity at low temperatures shows similar behavior observed for pure systems in applied field, of which gap energy decreases with increasing H.The results suggest that the ground state of the random-bond ladder is a Griffiths phase. Less

新的量子反铁磁链，自旋梯系统，吸引了大量的理论和实验的兴趣。偶数支梯被认为是自旋能隙系统，并且具有短程共振价键（RVB）基态。化合物Cu_2（C_5H_N_2<12>）_2Cl_4（以下简称CHpC）是一个典型的两足梯形体系，梯形的梯级（J_∞/k=13.2K）和梯形的腿（J _</>/k=2.4K）具有交换作用，自旋能Δ/k= 10.5K。最近，我们报道了一个新化合物Cu_2（C_5H_N_2）_2Br_4的实验结果<12>结果表明，CHpB是一个具有类似于CHpC的自旋带隙的自旋梯型体系，其交换作用J _（max）/k=24.8K，J _（max）/k=3.5K，自旋带隙能Δ/k = 21.3K，因此，CHpB的自旋带隙能与CHpC的自旋带隙能基本相同。无规混合物Cu_2（<12>C_5H_N_2）_2（Cl_<1-x>Br_x）_4似乎是一个具有无规反铁磁键梯形体系。的磁特性 ...更多信息无规混合化合物Cu_2（<12>C_5H_N_2）_2（Cl_<1-x>Br_x）_4与纯体系有较大的不同。顺磁发散是显着观察的磁化率在低温和磁化出现，即使在低场。对于随机系统，磁化率不遵循居里定律，并且发散比居里定律更强。具有强随机性的体系处于随机单态相或处于Griffice相，其磁化率在低温下发散。在低温下测量了纯体系和无规体系的热容。在纯系统的情况下，热容的行为是指数型的T^2exp（-Δ/kT），其中Δ是集体激发的差距能。对于无规体系，在低温下的热容表现出与纯体系在外加电场下相似的行为，其能隙随H的增加而减小。结果表明，无规键梯的基态是Griffiths相。少