Quantum critical state in a magnetic quasicrystal
Quantum critical state in a magnetic quasicrystal
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DOI：
10.1038/nmat3432
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发表时间：
2012-12-01
期刊：
影响因子：
41.2
通讯作者：
Ishimasa, Tsutomu
中科院分区：
文献类型：
--
作者：
Deguchi, Kazuhiko;Matsukawa, Shuya;Ishimasa, Tsutomu
准晶体是一种金属合金，具有长程非周期性结构，其衍射对称性是常规晶体所不允许的。自1984年谢赫特曼等人发现准晶体以来，在解析其几何结构方面已经取得了相当大的进展。例如，众所周知，数学和艺术中的黄金比例在其晶体结构中反复出现。然而，电子态的特性——它们是像周期晶体中那样扩展的，还是像非晶态材料中那样局域化的——仍然没有得到解决。在此我们报道了对金 - 铝 - 镱准晶体量子（T = 0）临界现象的首次观测——由镱原子的强关联4f电子引起的磁化率和电子比热系数在T -> 0时发散。此外，我们观察到这种量子临界现象对静水压力具有鲁棒性。相比之下，在一种晶体近似相中没有这种发散，该相的成分接近准晶体，其单胞具有看起来像准晶体的原子装饰（即二十面体原子团簇）。这些结果清楚地表明，量子临界性与准晶体独特的电子态相关，即一种空间受限的临界态。最后我们讨论了在常规晶体和准晶体之下存在一个普遍规律的可能性。
Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984(1), there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal-the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T -> 0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals.