World Premier International-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan.
Japan Science and Technology Agency, ERATO Isobe Degenerate π-Integration Project, Tohoku University, Sendai 980-8577, Japan.
Nat Chem. 2017 Jul;9(7):635-643. doi: 10.1038/nchem.2764. Epub 2017 Apr 24.
Molecular solids with cooperative electronic properties based purely on π electrons from carbon atoms offer a fertile ground in the search for exotic states of matter, including unconventional superconductivity and quantum magnetism. The field was ignited by reports of high-temperature superconductivity in materials obtained by the reaction of alkali metals with polyaromatic hydrocarbons, such as phenanthrene and picene, but the composition and structure of any compound in this family remained unknown. Here we isolate the binary caesium salts of phenanthrene, Cs(CH) and Cs(CH), to show that they are multiorbital strongly correlated Mott insulators. Whereas Cs(CH) is diamagnetic because of orbital polarization, Cs(CH) is a Heisenberg antiferromagnet with a gapped spin-liquid state that emerges from the coupled highly frustrated Δ-chain magnetic topology of the alternating-exchange spiral tubes of S = ½ (CH) radical anions. The absence of long-range magnetic order down to 1.8 K (T/J ≈ 0.02; J is the dominant exchange constant) renders the compound an excellent candidate for a spin-½ quantum-spin liquid (QSL) that arises purely from carbon π electrons.
基于碳原子的纯π电子的具有协同电子性质的分子固体为寻找奇异物质状态提供了肥沃的土壤，包括非常规超导性和量子磁性。该领域的研究始于报道在碱金属与多环芳烃（如菲和苝）反应得到的材料中存在高温超导性，但该家族中任何化合物的组成和结构仍然未知。在这里，我们分离出菲的二元铯盐 Cs(CH) 和 Cs(CH)，证明它们是多轨道强关联的莫特绝缘体。由于轨道极化，Cs(CH) 是抗磁性的，而 Cs(CH) 是一个具有能隙的自旋液体态的海森堡反铁磁体，它源于交替交换螺旋管中 S = ½ (CH)自由基阴离子的高度受挫 Δ 链磁拓扑结构的耦合。在 1.8 K 以下（T/J ≈ 0.02；J 是主要的交换常数）没有长程磁有序，使得该化合物成为纯粹由碳 π 电子产生的自旋-½ 量子自旋液体 (QSL) 的理想候选物。
