Low-Energy Magnetic Excitation of Kondo Semiconductor

核磁共振测量表明，近藤半导体CeNiSn磁激发过程中存在能隙。通过中子散射可以获得补充的和更直接的能隙证据，这是本研究的目的。然而，由于磁信号非常微弱，并且隐藏在较大的噪声中，因此很难观察到。为了解决这个问题，我们计划通过制备一种利用更大立体角的水平聚焦分析器来提高冷导三轴光谱仪的强度。利用计算机模拟对分析仪的几何形状进行了优化。测试实验表明，在相同能量分辨率的情况下，与以往的准直器条件相比，该分析器具有高达14倍的放大倍数。背景的减少对微弱信号也很重要，这是通过在分析器和检测器之间插入屏蔽件来实现的。通过聚焦分析器的这些努力，三轴光谱仪在强度和噪声方面的性能都有了很大的提高。用这台仪器测量了由同位素^&lt；58&gt；Ni组成的多晶状样品的低能磁激发。很明显，磁隙确实存在于1.5 meV以下的能量范围内。虽然1.5 meV的能量尺度比比热和核磁共振的预期值高出两到三倍，但光谱形状和温度依赖关系与核磁共振结果绝对一致。我们得出的结论是，本工作证明了磁激发的间隙。

The energy gap in the magnetic excitation of the Kondo semiconductor CeNiSn was shown by NMR measurements. Complementary and more direct evidence of the energy gap can be obtained by neutron scattering, which is the purpose of the present investigation. However, the magnetic signal is very difficult to observe, because it is very weak and hidden in larger noise. To resolve this problem we planned to increase the intensity of a cold-guide triple-axis spectrometer by preparing a horizontally focusing analyzer which utilizes a larger solid angle. The geometry of the analyzer was optimized using a computer simulation. Test experiments of the analyzer showed that it gives a large gain factor of 14 in intensity compared to the previous collimator condition with the same energy resolution. Reduction of background is also important for weak signals, and this was achieved by inserting a shield between the analyzer and the detector. By these efforts of the focusing analyzer, the performance of the triple-axis spectrometer was substantially improved in terms of both intensity and noise. Using this instrument we measured low-energy magnetic excitation on a polycrystal-like sample which is made of an isotope ^<58>Ni. It has been becoming clear that the magnetic gap really exists in an energy range below 1.5 meV.Although the energy scale of 1.5 meV is larger than the value expected from specific heat and NMR by a factor two or three, the spectral shape and the temperature dependence is definitely consistent with the NMR results. We conclude that the gap of the magnetic excitation is proved by the present work.