论文标题
通过稀土离子取代在无限层镍中调整的可能的结构量子临界。
Possible structural quantum criticality tuned by rare-earth ion substitution in infinite-layer nickelates
论文作者
论文摘要
我显示，通过使用第一个priniciples计算来绘制其结构不稳定性的能量，无限层稀土镍盐靠近结构量子临界点。我首先确认先前的结果，该结果显示了$ p4/mmm $相位的声子不稳定，导致$ i4/mcm $ $ $ nio $ _2 $ a $ r $ = sm-lu的$ i4/mcm $结构。然后，我研究了$ i4/mcm $相位的非自旋偏振声子分散剂，发现它们在$ x $ $ x $和$ m $点的材料上表现出稀有尺寸的依赖性不稳定性，其中$ r $ = eu-lu。由于这些稳定性，使用组理论分析来枚举所有各向同性亚组，并且使用不稳定声子的特征向量生成了与其顺序参数相对应的扭曲结构。然后通过最大程度地减少原子力和晶格应力来完全放松这些结构。我能够稳定在十二个可能的扭曲中五个。 $ pbcn $ ssotropy子组，带有$ M_5^+（a，a）$订单参数显示出相对于具有较晚稀土离子的化合物的其他扭曲，能量增益明显。但是，最低能量阶段的顺序参数首先切换为$ x_2^ - （0，a） + m_5^ +（b，0）$，然后$ x_2^ - （0，a）$，因为稀有地点的大小逐渐增加。此外，对于本系列的早期成员，几个扭曲的结构都靠近能量。即使允许抗铁磁性，结构能量的这些特征仍然存在。可以通过稀土离子替代来调整不同顺序参数之间的这种竞争表明，这些材料中存在的声子不稳定性可能引起的任何结构过渡都可以抑制为0 k。
I show the infinite-layer rare-earth nickelates are near a structural quantum critical point by mapping the energetics of their structural instabilities using first priniciples calculations. I first confirm previous results that show a phonon instability in the $P4/mmm$ phase leading to the $I4/mcm$ structure for $R$NiO$_2$ with $R$ = Sm--Lu. I then study the non-spin-polarized phonon dispersions of the $I4/mcm$ phase and find that they exhibit rare-earth size dependent instabilities at the $X$ and $M$ points for materials with $R$ = Eu--Lu. Group-theoretical analysis was used to enumerate all the isotropy subroups due to these instablities, and the distorted structures corresponding to their order parameters were generated using the eigenvectors of the unstable phonons. These structures were then fully relaxed by minimizing both the atomic forces and lattice stresses. I was able to stabilize only five out of the twelve possible distortions. The $Pbcn$ isotropy subgroup with the $M_5^+(a,a)$ order parameter shows noticeable energy gain relative to other distortions for the compounds with late rare-earth ions. However, the order parameter of the lowest-energy phase switches first to $X_2^- (0,a) + M_5^+ (b,0)$ and then to $X_2^- (0,a)$ as the size of the rare-earth ion is progressively increased. Additionally, several distorted structures lie close in energy for the early members of this series. These features of the structural energetics persist even when antiferromagnetism is allowed. Such a competition between different order parameters that can be tuned by rare-earth ion substitution suggests that any structural transition that could arise from the phonon instabilities present in these materials can be suppressed to 0 K.
