标题： 氘核相关运动的磁性证据对六甲基苯同位素效应的影响 显示英文标题

标题： Isotope Effect on the Magnetic Properties of Hexamethylbenzene: Evidence of Magnetism Based on Correlated Motion of Deuterons

摘要： 与六甲基苯C$_6$(CH$_3$)$_6$中甲基的周期性旋转运动相关的磁矩最近被确认为其整体磁化率的贡献。 然而，这些测量仅在含氢多晶样品上进行。 我们报告了在应用磁场平行和垂直于分子基底平面的情况下，单晶C$_6$(CH$_3$)$_6$的磁化率测量结果。 在前一种情况下，发现了接近起始温度T$_{C-H}$=118 K 的亚稳态行为，而在后一种情况下，未观察到异常行为。 在氘代六甲基苯 C$_6$(CD$_3$)$_6$ (其中 D 为氘) 中也观察到类似的异常，然而，T$_{C-D}$在 132 K 时高出 14 K。此外，靠近 42 K 处的一个峰异常被推测是由于氘核相干量子隧穿的开始。 近立方基态被提出是由于在分子固体中发生的一种更激进的 Jahn-Teller 效应，晶格畸变以消除质子的轨道简并性从而降低其能量。 明显的磁各向异性和同位素效应提供了证据，表明除了电子之外，不仅质子，而且氘核也表现出强烈的关联行为。 显示英文摘要

摘要： The associated magnetic moments of the periodic rotational motion of methyl groups in hexamethylbenzene C$_6$(CH$_3$)$_6$ were recently identified to contribute to its overall magnetic susceptibility. Those measurements however, were only performed on hydrogenous polycrystalline samples. We report magnetic susceptibility measurements on single crystalline C$_6$(CH$_3$)$_6$ in the cases where the applied magnetic field is parallel and perpendicular to the molecular basal planes. In the former case, metastable behavior near the onset temperature T$_{C-H}$=118 K is identified while in the latter, no anomalous behavior is observed. Similar anomalies are observed in deuterated hexamethylbenzene C$_6$(CD$_3$)$_6$ (where D is deuterium), however, T$_{C-D}$ occurs 14 K higher at 132 K. In addition, a peak anomaly identified near 42 K is suggested to be due to the onset of coherent quantum tunneling of deuterons. The near cubic ground state is proposed to be the result of a more radical form of the Jahn-Teller effect occurring in a molecular solid where the lattice distorts to remove the orbital degeneracies of the protons to lower its energy. The apparent magnetic anisotropy and isotope effect provide evidence that apart from electrons, not only protons, but also deuterons establish strongly correlated behavior.