Direct observation of lattice symmetry breaking at the hidden-order transition in URu2Si2
Direct observation of lattice symmetry breaking at the hidden-order transition in URu2Si2
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DOI：
10.1038/ncomms5188
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发表时间：
2014-06
影响因子：
16.6
通讯作者：
S. Tonegawa;S. Kasahara;T. Fukuda;K. Sugimoto;N. Yasuda;Y. Tsuruhara;D. Watanabe;Y. Mizukami
中科院分区：
文献类型：
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作者：
S. Tonegawa;S. Kasahara;T. Fukuda;K. Sugimoto;N. Yasuda;Y. Tsuruhara;D. Watanabe;Y. Mizukami
自从1985年在重费米子金属URU2Si2中发现了THO=17.5K的相变以来，既没有观察到晶体结构的对称性变化，也没有观察到可以解释这一熵变的大磁矩，这使得这个隐藏的有序成为一个谜。最近的高场实验表明，电子的向列性破坏了四重旋转对称性，但在没有磁场的情况下，还缺乏关于它的基态的直接证据。本文报道了用零场高分辨率同步加速器X射线衍射法观察到晶格对称性从四重四方结构向二重正交体结构的断裂，从而确定了该有序的空间对称性。带有跳跃的atTHO中的小的正交对称破缺扭曲集，揭示了隐藏有序跃迁的弱一阶性质。这种扭曲只在超纯样品中观察到，这意味着电子向列性和底层晶格之间存在非常不寻常的耦合性质。
Since the 1985 discovery of the phase transition atTHO=17.5 K in the heavy-fermion metal URu2Si2, neither symmetry change in the crystal structure nor large magnetic moment that can account for the entropy change has been observed, which makes this hidden order enigmatic. Recent high-field experiments have suggested electronic nematicity that breaks fourfold rotational symmetry, but direct evidence has been lacking for its ground state in the absence of magnetic field. Here we report on the observation of lattice symmetry breaking from the fourfold tetragonal to twofold orthorhombic structure by high-resolution synchrotron X-ray diffraction measurements at zero field, which pins down the space symmetry of the order. Small orthorhombic symmetry-breaking distortion sets in atTHOwith a jump, uncovering the weakly first-order nature of the hidden-order transition. This distortion is observed only in ultrapure samples, implying a highly unusual coupling nature between the electronic nematicity and underlying lattice.