Spin Nematic State as a Candidate of the Hidden Order Phase of ${\mathrm{URu}}_2{\mathrm{Si}}_2$

Motivated by the recent discovery of broken fourfold symmetry in the hidden order phase of ${\mathrm{URu}}_2{\mathrm{Si}}_2$ [R. Okazaki et al., Science 331, 439 (2011)], we examine a scenario of a spin nematic state as a possible candidate of the hidden order phase. We demonstrate that the scenario naturally explains most of experimental observations, and furthermore, reproduces successfully the temperature dependence of the spin anisotropy detected by the above-mentioned experiment in a semiquantitative way. This result provides strong evidence for the realization of the spin nematic order.

Figure 1

(a) Solid line: anisotropy of the spin susceptibility $\Delta \chi ={\chi }_{x^{\prime }{x}^{\prime }}-{\chi }_{y^{\prime }{y}^{\prime }}$ in the SN phase versus $T/T_{\mathrm{HO}}$. The magnitude of $\Delta \chi$ is normalized by the value at $T=0$. Circle: experimental data quoted from 25. ${\Delta }_1(0)/T_{\mathrm{HO}}=2.6$. (b) $\mathrm{Im}{\chi }^{zz}({\mathit{Q}}_0,\omega )$ versus $\omega /{\Delta }_1$. ${\mu }_{\mathrm{B}}{H}_z/{\Delta }_1=0$ (solid), 0.1 (dotted), 0.2 (dashed), 0.3 (dot-dashed), 0.4 (double-dot-dashed). (c) $\mathrm{Im}{\chi }^{zz}({\mathit{Q}}_1,\omega )$ versus $\omega /{\Delta }_1$. ${\mu }_{\mathrm{B}}{H}_z/{\Delta }_1=0$ (solid), 0.1 (dotted), 0.2 (dashed), 0.3 (dot-dashed).