Sarte P M, Wilson S D, Attfield J P, Stock C
California NanoSystems Institute, University of California, Santa Barbara, California 93106-6105, United States of America.
Materials Department, University of California, Santa Barbara, California 93106-5050, United States of America.
J Phys Condens Matter. 2020 Jun 18;32(37). doi: 10.1088/1361-648X/ab8498.
Motivated by the presence of an unquenched orbital angular momentum in CoO, a team at Chalk River, including a recently hired research officer Roger Cowley, performed the first inelastic neutron scattering experiments on the classic Mott insulator [Sakurai1968510]. Despite identifying two magnon modes at the zone boundary, the team was unable to parameterise the low energy magnetic excitation spectrum belowusing conventional pseudo-bosonic approaches, instead achieving only qualitative agreement. It would not be for another 40 years that Roger, now at Oxford and motivated by the discovery of the high-cuprate superconductors [Bednorz and Muller 1986189], would make another attempt at the parameterisation of the magnetic excitation spectrum that had previously alluded him at the start of his career. Upon his return to CoO, Roger found a system embroiled in controversy, with some of its most fundamental parameters still remaining undetermined. Faced with such a formidable task, Roger performed a series of inelastic neutron scattering experiments in the early 2010s on both CoO and a magnetically dilute structural analogue MgCoO. These experiments would prove instrumental in the determination of both single-ion [Cowley2013205117] and cooperative magnetic parameters [Sarte2018024415] for CoO. Both these sets of parameters would eventually be used in a spin-orbit exciton model [Sarte2019075143], developed by his longtime friend and collaborator Bill Buyers, to successfully parameterise the complex spectrum that both measured at Chalk River almost 50 years prior. The story of CoO is of one that has come full circle, one filled with both spectacular failures and intermittent, yet profound, little victories.
受氧化钴中未淬灭的轨道角动量的影响，查克里河的一个团队，包括最近聘用的研究人员罗杰·考利，对经典的莫特绝缘体进行了首次非弹性中子散射实验[Sakurai1968510]。尽管该团队在区域边界处识别出了两种磁振子模式，但他们无法使用传统的准玻色子方法对低能磁激发谱进行参数化，只能得到定性的结果。直到40年后，罗杰（此时他在牛津大学，受高温铜酸盐超导体发现的启发[贝德诺尔茨和米勒1986189]）才再次尝试对他职业生涯初期未能解决的磁激发谱进行参数化。回到氧化钴的研究中，罗杰发现这个体系陷入了争议，一些最基本的参数仍然没有确定。面对如此艰巨的任务，罗杰在21世纪10年代初对氧化钴和磁性稀释的结构类似物MgCoO进行了一系列非弹性中子散射实验。这些实验对于确定氧化钴的单离子[考利2013205117]和协同磁参数[萨特2018024415]起到了重要作用。这两组参数最终都被用于他的长期朋友兼合作者比尔·拜尔斯开发的自旋轨道激子模型[Sarte2019075143]中，成功地对近50年前在查克里河测量的复杂光谱进行了参数化。氧化钴的故事是一个循环往复的故事，充满了巨大的失败以及断断续续却意义深远的小胜利。
