| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 1998: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1997: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
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.
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