Yanagisawa T, Matsumori H, Saito H, Hidaka H, Amitsuka H, Nakamura S, Awaji S, Gorbunov D I, Zherlitsyn S, Wosnitza J, Uhlířová K, Vališka M, Sechovský V
Department of Physics, Hokkaido University, Sapporo 060-0810, Japan.
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Phys Rev Lett. 2021 Apr 16;126(15):157201. doi: 10.1103/PhysRevLett.126.157201.
We present acoustic signatures of the electric quadrupolar degrees of freedom in the honeycomb-layer compound UNi_{4}B. The transverse ultrasonic mode C_{66} shows softening below 30 K both in the paramagnetic phase and antiferromagnetic phases down to ∼0.33 K. Furthermore, we traced magnetic field-temperature phase diagrams up to 30 T and observed a highly anisotropic elastic response within the honeycomb layer. These observations strongly suggest that Γ_{6}(E_{2g}) electric quadrupolar degrees of freedom in localized 5f^{2} (J=4) states are playing an important role in the magnetic toroidal dipole order and magnetic-field-induced phases of UNi_{4}B, and evidence some of the U ions remain in the paramagnetic state even if the system undergoes magnetic toroidal ordering.
我们展示了蜂窝层化合物UNi₄B中电四极自由度的声学特征。横向超声模式C₆₆在顺磁相和低至约0.33 K的反铁磁相中，在30 K以下均表现出软化。此外，我们绘制了高达30 T的磁场-温度相图，并观察到蜂窝层内高度各向异性的弹性响应。这些观察结果强烈表明，局域5f²（J = 4）态中的Γ₆（E₂g）电四极自由度在UNi₄B的磁环形偶极序和磁场诱导相中起着重要作用，并且证明即使系统经历磁环形有序，一些U离子仍保持顺磁状态。
