New ordered states and response to dynamical field of strongly fluctuating quantum systems

新有序态及对强涨落量子系统动力场的响应

• 批准号: 10640368
• 负责人: MIYASHITA Seiji
• 金额: $ 1.79万
• 依托单位: The University of Tokyo (1999)Osaka University (1998)
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1998
• 资助国家: 日本
• 起止时间: 1998 至 1999
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640368/
• 关键词: quantum spin system; quantum Monte Carlo; nanoscale magnets; ESR; nonadiabatic transition; photoinduced phasetransition; ESP; 量子揺動; 量子相転移; 量子ダイナミックス; ESR

We have investigated the local magnetic structures of quantum spin systems induced by inhomogeneity of the lattice mainly by the quantum Monte Carlo method. In particularly, the S=1/2 doped S=1 antiferromagnetic Heisenberg model (Haldane system), the bond random S=1/2 antiferromagnetic Heisenberg model (gapless system) and the bond alternate S=1/2 antiferromagnetic Heisenberg model (dimer system) with a defect of the alternation. We also investigated the mechanism of ferromagnetism in the itinerant electron system (Hubbard model) and found a new type of mechanism. We also developed a new direct numerical method to study the line shape of ESR in strongly interacting quantum spin systems, and investigate the dynamical shift due to the dipole interaction, anisotropy and DM interactions. We have studied the following phenomena in which the quantum dynamics plays an important role. We investigated the quantum hysteresis phenomena in nanoscale molecular magnets such as Mn12, Fe8 and V15 in the view point of non adiabatic transition. We studied the effects of the environments, such as the phonon, the dipole interaction and hyperfine interactions with the nuclear spins, on the quantum dynamics. In particular, we clarified mechanisms of deceptive non-adiabatic transition at very low temperature, of the parity effect due to the thermally excited states and of the quantum foehn phenomena due to inflow of the heat.

本文主要用量子蒙特卡罗方法研究了晶格非均匀性诱导的量子自旋系统的局部磁结构。其中，S=1/2掺杂S=1反铁磁海森堡模型（Haldane体系）、键随机S=1/2反铁磁海森堡模型（无间隙体系）和键交替S=1/2反铁磁海森堡模型（二聚体体系）存在交替缺陷。我们还研究了流动电子系统（Hubbard模型）中的铁磁性机制，发现了一种新的机制。我们还开发了一种新的直接数值方法来研究强相互作用量子自旋系统中ESR的线形，并研究了由偶极相互作用、各向异性和DM相互作用引起的动力学位移。我们研究了以下现象，其中量子动力学起着重要作用。从非绝热跃迁的角度研究了纳米级分子磁体Mn12、Fe8和V15的量子滞后现象。我们研究了声子、偶极子相互作用以及与核自旋的超精细相互作用等环境对量子动力学的影响。特别地，我们阐明了极低温下欺骗性非绝热跃迁的机制、热激发态引起的宇称效应和热流入引起的量子胀风现象。

项目成果

Keiji Saito et al.: "Effects of the environment on nonadiabatic magnetization process in uniaxial molecular magnets at very low temperatures"Phys. Rev. B. 60.21. 14553-14556 (1999)

Keiji Saito 等人：“环境对极低温下单轴分子磁体非绝热磁化过程的影响”Phys.

Yuuki Watanabe et al.: "Existence of Saturated Ferromagnetic and Spiral States in 1D Lieb-Ferrimagnetic Model away from Half-Filling."J. Phys. Soc. Jpn.. 68, 9. 3086-3090 (1999)

Yuuki Watanabe 等人：“远离半填充的一维 Lieb-亚铁磁模型中饱和铁磁和螺旋态的存在”。

Masamichi Nishino et al.: "Local magnetic structure due to inhomogeneity of interaction in S=1/2 antiferromagnetic chain"Phys. Rev. B. 61.6. 4033-4040 (2000)

Masamichi Nishino 等人：“由于 S=1/2 反铁磁链中相互作用的不均匀性而导致的局部磁性结构”Phys。

Keiji Saito et al.: "Effects of the environment on nonadiabatic magnetization process in uniaxial molecular magnets at very low temperature"Physical Review B. 60・21. 14553-14556 (1999)

Keiji Saito 等：“环境对极低温下单轴分子磁体非绝热磁化过程的影响”Physical Review B. 60・21 (1999)。

Masamichi Nishino et al.: "Local magnetic structure clue to inhomogeneity of interaction in S=1/2 antiferromagnetic chain"Phys. Rev. B. 61, 6. (2000)

Masamichi Nishino 等人：“局部磁结构提示 S=1/2 反铁磁链中相互作用的不均匀性”Phys。