Study of single-crystal spectroscopy with pulsed neutrons

在本研究项目中，建立了单晶样品的脉冲中子中子能谱，并研究了低维系统中的自旋动力学。自旋为3/2的ID Heisenberg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。我们在整个布里渊区测出了低温下的S （q,）区域边界能量为75 meV，这可以用量子重正化因子磁化率测量的交换常数(J)来解释，能量宽度（GAMMA）在较大的q下是恒定的。我们测量了GAMMA在较大的q下的温度(T)依赖性，其中GAMMA在低T下与q无关，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，正如经典理论所预测的那样，然而，在低T （>J）时，GAMMA是有限的，尽管kappa仍然具有线性T依赖性。最近对一个低温度下的自旋-3/2系统进行了数值计算，预测了磁区中心的激发连续统的能量扩展约为J，我们观察到相应的能量扩展。因此，低T处的有限γ是由激发连续体引起的。如上所述，在激发能中也存在量子重整化。因此，在低温度下，自旋为3/2的系统表现出量子行为。我们发现一个自旋-3/2的系统表现出从低T的量子态到高T的经典态的交叉，并且交叉发生在可观测的T范围内。

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.