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Study of single-crystal spectroscopy with pulsed neutrons

脉冲中子单晶光谱研究

基本信息

批准号：
09640449
负责人：
ITOH Shinichi
金额：
$ 2.37万
依托单位：
HIGH ENERGY ACCELERATOR RESEARCH ORGANIZATION
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640449/
关键词：
pulsed neutrons neutron scattering low-dimensional magnetism spin dynamics single crystals

项目摘要

In this research project, a neutron spectroscopy for a single-crystal sample with pulsed neutrons was developed and the spin dynamics in low-dimensional systems was studied. ID Heisenberg antiferromagnetic systems with spin-3/2, CsVCl^3 and CsVBr^3, are suitable for investigating a crossover from the quantum limit for lower spin systems to the classlibal limit for larger spin systems. We determined S (q, omega) at low temperature at the entire Brillouin zone. The zone boundary energy was determined to be 75 meV, which can be explained by the exchange constant (J) from the susceptibility measurement with a quantum renormalization factor, and the energy widths (GAMMA) were found to be constant at larger q. We measured the temperature (T) dependence of GAMMA at larger q, where GAMMA is independent of q at the low T, and also measured the T-dependence of the inverse magnetic correlation length (kappa(T)). At high T (>J), GAMMA and kappa are proportional to T, as predicted by classical theory, however, at low T (>J), GAMMA is finite although kappa still has the linear T-dependence. A recent numerical calculation for a spin-3/2 system at low T has predicted an excitation continuum with an energy spread up to about J at the magnetic zone center, and we observed the corresponding energy spread. Therefore the finite GAMMA at low T is caused by the excitation continuum. As mentioned above, there also exists the quantum renormalization in the excitation energy. Therefore at low T, a spin-3/2 system shows quantum behavior. We found a spin-3/2 system exhibits the crossover from the quantum state at low T to the classical state at high T, and the crossover occurs at an observable T-range.

在本研究计画中，我们发展了一个单晶样品的脉冲中子能谱，并研究了低维系统的自旋动力学。自旋为3/2的1D海森堡反铁磁系统CsVCl^3和CsVBr^3适合于研究从低自旋系统的量子极限到大自旋系统的经典极限的交叉。我们在低温下在整个布里渊区测定了S（q，ω）。区域边界能量被确定为75 meV，这可以通过具有量子重整化因子的磁化率测量的交换常数（J）来解释，并且发现能量宽度（Gamma）在较大的q处是恒定的。我们测量了在较大q下的温度（T）依赖性，其中在低T下，Gamma与q无关，并且还测量了逆磁相关长度（kappa（T））的T依赖性。在高T（>J）时，Gamma和kappa与T成正比，这与经典理论的预测一致;而在低T（>J）时，Gamma是有限的，但kappa仍与T成线性关系。最近的一个数值计算自旋3/2系统在低T预测的激发连续谱的能量扩展到约J的磁区中心，我们观察到相应的能量扩展。因此，低T下的有限Gamma是由激发连续谱引起的。如上所述，在激发能中也存在量子重整化。因此，在低T下，自旋3/2系统显示量子行为。我们发现一个自旋为3/2的系统表现出从低T量子态到高T经典态的跃迁，并且跃迁发生在可观测的T范围内。