论文标题
eual4的四方晶格上的矫正电荷密度波
Orthorhombic charge density wave on the tetragonal lattice of EuAl4
论文作者
论文摘要
Eual4具有带有四方对称性i4/mmm的Baal4晶体结构类型。它在TCDW = 145 K处进行电荷密度波（CDW）过渡，并且在16 K以下具有四个连续的抗铁磁相变。 CDW与调节波矢量Q =（0，0，0，0.1781（3））在70K处是不均匀的。不相互调制的晶体结构的对称性与超空间组FMMM（00σ）s00的superspace群（00σ）s00，fmmm是I4/mmm of Index 2的子群，同时又是INDEX 2的子组。四方。对称断裂完全是由于调制波，其中原子欧盟和AL1仅沿A位移，而四倍旋转将需要沿A和B的相等位移幅度。调制晶体结构中基本结构和原子间距离的计算带结构都表示铝原子作为CDW的位置。特异性热的温度依赖性显示在TCDW = 145 k的幅度类似于规范CDW系统时发生异常。目前针对CDW eual4状态的正常对称性的发现导致了单斜骨的建议，而不是第三AFM状态的单斜晶状体对称性。
EuAl4 possesses the BaAl4 crystal structure type with tetragonal symmetry I4/mmm. It undergoes a charge-density-wave (CDW) transition at TCDW = 145 K and it features four consecutive antiferromagnetic phase transitions below 16 K. Here, we use single-crystal x-ray diffraction to determine incommensurately modulated crystal structure of EuAl4 in its CDW state. The CDW is shown to be incommensurate with modulation wave vector q = (0, 0, 0.1781(3)) at 70 K. The symmetry of the incommensurately modulated crystal structure is orthorhombic with superspace group Fmmm(00σ)s00, where Fmmm is a subgroup of I4/mmm of index 2. Both the lattice and the atomic coordinates of the basic structure remain tetragonal. Symmetry breaking is entirely due to the modulation wave, where atoms Eu and Al1 have displacements exclusively along a, while the fourfold rotation would require equal displacement amplitudes along a and b. The calculated band structure of the basic structure and interatomic distances in the modulated crystal structure both indicate the aluminum atoms as location of the CDW. The temperature dependence of the specific heat reveals an anomaly at TCDW = 145 K of a magnitude similar to canonical CDW systems. The present discovery of orthorhombic symmetry for the CDW state of EuAl4 leads to the suggestion of monoclinic instead of orthorhombic symmetry for the third AFM state.
