We present experimental evidence for a quantum phase transition in the easy-axis $S=3/2$ anisotropic quasi-one-dimensional ferromagnet ${\mathrm{CoCl}}_2·2{\mathrm{D}}_2\mathrm{O}$ in a transverse field. Elastic neutron scattering shows that the magnetic order parameter vanishes at a transverse critical field ${\mu }_0{H}_c=16.05$(4) T, while inelastic neutron scattering shows that the gap in the magnetic excitation spectrum vanishes at the same field value, and reopens for $H>H_c$. The field dependence of the order parameter and the gap are well described by critical exponents $\beta =0.45\pm 0.09$ and $z\nu$ close to $1/2$, implying that the quantum phase transition in ${\mathrm{CoCl}}_2·2{\mathrm{D}}_2\mathrm{O}$ differs significantly from the textbook version of a $S=1/2$ Ising chain in a transverse field. We attribute the difference to weak but finite three-dimensionality of the magnetic interactions.

中文翻译：

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横向场中准一维Ising型铁磁体CoCl2·2D2O的自旋激发和量子临界

我们提供了易轴上量子相变的实验证据 $\mathrm{小号}=3/\mathrm{2个}$ 各向异性准一维铁磁体 ${\mathrm{氯化钴}}_{\mathrm{2个}}·\mathrm{2个}{\mathrm{d}}_{\mathrm{2个}}\mathrm{Ø}$在横向领域。弹性中子散射表明，磁阶参数在横向临界场处消失${\mu }_0{H}_C=16.05$（4）T，而非弹性中子散射表明，在相同的场值下，磁激发光谱中的间隙消失了，并且对于 $H>H_C$。关键参数很好地描述了阶数参数和间隙的场相关性$\beta =0.45\pm 0.09$ 和 $ž\nu$ 相近 $\mathrm{1个}/\mathrm{2个}$，暗示量子相变在 ${\mathrm{氯化钴}}_{\mathrm{2个}}·\mathrm{2个}{\mathrm{d}}_{\mathrm{2个}}\mathrm{Ø}$ 与教科书版本的 $\mathrm{小号}=\mathrm{1个}/\mathrm{2个}$伊辛链在横向领域。我们将差异归因于磁性相互作用的弱但有限的三维性。