NdNiO $_3$超晶格中隐基态有序的控制
Control of hidden ground-state order in NdNiO$_3$ superlattices
摘要：
在凝聚态系统中，电荷和自旋自由度与电子相关性的结合导致了一系列丰富的现象，如磁性，超导性和新的传导机制。虽然在体材料中观察到了这种现象，但当这些自由度在原子分层异质结构中受到控制时，可能会出现更丰富的行为，其中可以限制维度并施加界面边界条件。在这里，我们解锁了主机的独特的，隐藏的电子和磁性相变在NdNiO $_3$，同时接近二维（2D）的限制，从不同的尺寸限制和界面耦合的影响。最值得注意的是，我们发现了一个新的阶段，在全二维，单层NdNiO $_3$，其中所有签名的散装磁性和电荷订购被发现消失。此外，对于准二维层的厚度下降到两个单位电池，批量型订购持续，但分开的绝缘行为的发病方式不同的散装或薄膜镍酸盐。使用共振X射线光谱，第一性原理理论和模型计算，我们提出，单层相抑制的结果从一个新的机制，界面电子重建的基础上跨界面的离子性差异，而在多层NdNiO $_3$的相分离出现由于增强的二维波动。这些发现提供了深入了解的相互交织的机制，在强相关的系统中，在减少的维度和说明使用原子分层访问隐藏的阶段的能力。
英文摘要：
The combination of charge and spin degrees of freedom with electronic correlations in condensed matter systems leads to a rich array of phenomena, such as magnetism, superconductivity, and novel conduction mechanisms. While such phenomena are observed in bulk materials, a richer array of behaviors becomes possible when these degrees of freedom are controlled in atomically layered heterostructures, where one can constrain dimensionality and impose interfacial boundary conditions. Here, we unlock a host of unique, hidden electronic and magnetic phase transitions in NdNiO$_3$ while approaching the two-dimensional (2D) limit, resulting from the differing influences of dimensional confinement and interfacial coupling. Most notably, we discover a new phase in fully 2D, single layer NdNiO$_3$, in which all signatures of the bulk magnetic and charge ordering are found to vanish. In addition, for quasi two-dimensional layers down to a thickness of two unit cells, bulk-type ordering persists but separates from the onset of insulating behavior in a manner distinct from that found in the bulk or thin film nickelates. Using resonant x-ray spectroscopies, first-principles theory, and model calculations, we propose that the single layer phase suppression results from a new mechanism of interfacial electronic reconstruction based on ionicity differences across the interface, while the phase separation in multi-layer NdNiO$_3$ emerges due to enhanced 2D fluctuations. These findings provide insights into the intertwined mechanisms of charge and spin ordering in strongly correlated systems in reduced dimensions and illustrate the ability to use atomic layering to access hidden phases.
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