BaCo$_2$(AsO$_4$)$_2$（BCAO）是一种蜂窝状钴酸盐，被认为是展现Kitaev量子自旋液体态的有前景的候选材料。这一假设基于Co$^{2+}$离子（3$d^7$）在八面体晶体环境中的独特特征，该环境导致自旋-轨道耦合的$J_{\ m eff}$=1/2双重态。然而，最近的实验观测和理论分析对这一假设提出了质疑。尽管存在这些不确定性，关于类似自旋子激发的连续激发的报道促使了进一步的研究。在本研究中，我们利用直流和交流磁化率、电容以及扭矩磁强测量，探索了BCAO在面内和面外磁场下的磁性相。我们的结果证实了多个场致磁性相的存在，且面内与面外磁场之间的相边界具有很强的各向异性。为了阐明这些相的本质，我们建立了一个最小各向异性交换模型。该模型在结合第一性原理计算和理论建模的支持下，定量地重现了我们的实验数据。在BCAO中，强键无关XXZ各向异性与几何阻挫的结合导致了显著的量子序由无序效应，在零磁场和有限磁场下稳定了共线相。
英文摘要：
BaCo$_2$(AsO$_4$)$_2$ (BCAO), a honeycomb cobaltate, is considered a promising candidate for materials displaying the Kitaev quantum spin liquid state. This assumption is based on the distinctive characteristics of Co$^{2+}$ ions (3$d^7$) within an octahedral crystal environment, resulting in spin-orbit-coupled $J_{\rm eff}$~=~1/2 doublet states. However, recent experimental observations and theoretical analyses have raised questions regarding this hypothesis. Despite these uncertainties, reports of continuum excitations reminiscent of spinon excitations have prompted further investigations. In this study, we explore the magnetic phases of BCAO under both in-plane and out-of-plane magnetic fields, employing dc and ac magnetic susceptibilities, capacitance, and torque magnetometry measurement. Our results affirm the existence of multiple field-induced magnetic phases, with strong anisotropy of the phase boundaries between in-plane and out-of-plane fields. To elucidate the nature of these phases, we develop a minimal anisotropic exchange model. This model, supported by combined first principles calculations and theoretical modeling, quantitatively reproduces our experimental data. In BCAO, the combination of strong bond-independent XXZ anisotropy and geometric frustration leads to significant quantum order by disorder effects that stabilize collinear phases under both zero and finite magnetic fields.
Ab initio guided minimal model for the "Kitaev" material BaCo$_2$(AsO$_4$)$_2$: Importance of direct hopping, third-neighbor exchange and quantum fluctuations
Field-induced first order transitions and phase coexistence in the Kitaev quantum spin liquid candidate BaCo2(AsO4)2
Rice University（赖斯大学）；Department of Physics and Astronomy, Rice University（赖斯大学物理与天文学系）；Rice Laboratory for Emergent Magnetic Materials and Smalley-Curl Institute, Rice University（赖斯大学涌现磁性材料实验室及Smalley-Curl研究所）；Department of Physics and Center for Quantum Frontiers of Research & Technology (QFort), National Cheng Kung University（国立成功大学物理系及量子前沿研究与技术中心）；Department of Physics, Boston College（波士顿学院物理系）；Australian Nuclear Science and Technology Organization (ANSTO)（澳大利亚核科学与技术组织）
Mechanism of Incommensurate Magnetic Order in $\mathrm{BaCo_2(AsO_4)_2}$: Interplay of Frustrated Further-Neighbor Exchanges and Bond-Directional Anisotropy
Qom University of Technology（库姆理工大学）；University of Toronto（多伦多大学）；Shahrekord University（沙赫里克尔德大学）
Zeeman split Kramers doublets in spin-supersolid candidate Na$_{2}$BaCo(PO$_{4}$)$_{2}$
School of Physics and Astronomy, University of Edinburgh（爱丁堡大学物理与天文学院）；ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory（STFC卢瑟福阿普尔顿实验室ISIS脉冲中子与缪子源）；NIST Center for Neutron Research（美国国家标准与技术研究院中子研究中心）；Department of Chemistry, Princeton University（普林斯顿大学化学系）
Comparative Raman Scattering Study of Crystal Field Excitations in Co-based Quantum Magnets
Wake Forest University（维克森林大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；National High Magnetic Field Laboratory（国家高磁场实验室）；Princeton University（普林斯顿大学）；University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校）；Georgia Institute of Technology（佐治亚理工学院）
Order-by-disorder from Schwinger bosons in a frustrated honeycomb ferromagnet
Institut Néel, Université Grenoble Alpes and CNRS（内尔研究所，格勒诺布尔阿尔卑斯大学和法国国家科学研究中心）；Departamento de Física Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid（凝聚态物理理论系，凝聚态物理中心（IFIMAC）和尼古拉斯·卡布雷拉研究所，马德里自治大学）
