Reinvestigation of spin-density wave of metallic Cr by neutron scattering-Search for a connection to stripe order--

1.用中子非弹性散射表征了新型低能磁激发铬的Fincher-Burke模(FB模)。令人惊讶的是，磁峰强度和磁色散关系都是围绕磁区中心不对称的。另一种铬单晶使用不同的仪器分辨率再现了这一显著特征，并且这种不对称性随着温度的升高而变得不那么明显。因此，我们得出结论，这种不对称性是FB模的固有性质，或者有另一个因素控制着这种不对称性(例如手性)。为了进一步研究，我们尝试观察了Mn/V杂质对FB模的影响。我们用电弧法成功地生长出了尺寸为1 mm的这种单晶。通过调整生长条件，它将能够生长出高达10 mm的杂质晶体，用于非弹性中子散射实验。通过对La2-xSrxCuO4(LSCO)中Ni杂质的掺杂，我们发现载流子浓度控制着磁关联和电输运。这类似于杂质掺杂在铬上的情况，在这种情况下，自旋关联的不可公度与杂质浓度(或带-电子密度)成正比。然而，在LSCO中还没有观察到像Cr中的FB模那样的磁激发。是否有这样的磁激发本质上是没有的，只是截面很小才能探测到，还是S(Q，E)在铬和氯化锂之间有很大的不同，这一争论是有必要的。在研究铬和LSCO的中子散射过程中，要求中子谱仪具有较高的S/N比和较高的Q分辨率。我们开发了一种结合使用Ge单色仪和幽门裂解石墨分析仪进行非弹性散射测量的新技术。事实上，我们用高的Q分辨率和合理的统计，成功地观测到了铬和LSCO的准粒子激发，如声子和磁子。

1. We characterized novel low-energy magnetic excitations of Cr, so-called Fincher-Burke mode (FB-mode), by neutron inelastic scattering. Surprisingly, both the magnetic-peak intensity and the magnetic-dispersion relation are found to be asymmetric about the magnetic-zone center. Another single crystal of Cr reproduces this prominent feature using different instrumental resolutions, and the asymmetry becomes less significant with increasing temperature. Thus, we concluded that such the asymmetry is an intrinsic nature of the FB mode, or that there is another factor governing this asymmetry (e. g. chirality). In order to investigate further, we tried to observe Mn/V-impurity effects on the FB mode. We succeeded in growing such the single crystals in 1-mm size by arc-melting techniques. By tuning the growing condition, it will be able to grow impurity-doped crystals up to 10 mm for inelastic neutron scattering experiments.2. Through Ni-impurity doping onto La2-xSrxCuO4 (LSCO), we found that carrier concentration governs magnetic correlations as well as electric transport. This is analogous to the case of impurity doping on Cr, in which the incommensurability of spin correlations is proportional to impurity concentration (or, band-electron density). However, no magnetic excitations like the FB mode in Cr are observable yet in LSCO. It is necessary to narrow an argument whether there are no such magnetic excitations intrinsically, the cross section is just small to detect, or S(Q, E) is quite different between Cr and LSCO.3. During the course of neutron-scattering research for Cr and LSCO, a high S/N ratio and a fine Q resolution are required in neutron spectrometer. We developed a new technique that uses a combination of a Ge monochromator and a pylorytic-graphite analyzer in inelastic scattering measurements. In fact, we succeeded in observing quasi-particle excitations, such as phonons and magnons, for Cr and LSCO with high Q resolutions and reasonable statistics.