Defects in graphene, such as vacancies or adsorbents attaching themselves to carbons, may preferentially take positions on one of its two sublattices, thus breaking the global lattice symmetry. This leads to opening a gap in the electronic spectrum. We show that such a sublattice ordering may spontaneously occur in a dilute ensemble defects, due to the long-range interaction between them mediated by electrons. As a result sublattice-ordered domains may form, with electronic properties characteristic of a two-dimensional topological insulator.
Anomalous magnetic ordering in PrBa_2Cu_3O_{7-y} single crystals: Evidence for magnetic coupling between the Cu and Pr sublattices
在无Al的O_{7-y}单晶中，与Pr反铁磁有序有关的磁化率chi_{ab}（T）随温度变化的扭折，在磁场H中场冷（FC）后消失||AB平面。在H的FC之后，chi_c（T）的扭结保持不变||c轴。作为一种可能的解释，位于ab平面的Cu磁矩的冻结是由H中的FC引起的||ab阻碍了它们的重取向，并且由于Pr和Cu（2）子晶格之间的耦合，阻碍了Pr^{3+}矩的有序化。对H和Pr^{3+}，都发现了场诱导的相变和Pr^{3+}有序温度的场依赖性||c和H|| AB.
Theory of Two-Step Magnetic Ordering Phenomena in a Geometrically Frustrated Heisenberg Pyrochlore Antiferromagnet with Long Range Dipolar Interactions
利用平均场论研究了具有交换作用和偶极-偶极相互作用的烧绿石晶格上的海森堡反铁磁体模型。在处理偶极通过使用埃瓦尔德方法，一个软（临界）模式与一个独特的有序波矢量被选择为所有强度的偶极偶极耦合。对于弱偶极子，选择部分有序的三个子晶格自旋结构（P态），其中q_{ord} =（1/2 1/2 1/2）。一个完全有序的四个子晶格自旋结构（F态），q =（000），与P态竞争，并随着温度的降低而成为稳定的结构。我们的结果进行了比较，对其他的理论计算和连接到最近的实验结果Gd 2 Ti 2 O 7进行了讨论。
The formation and dynamics of a wide variety of binary two-dimensional ordered structures and superlattices are investigated through a phase field crystal model with sublattice ordering. Various types of binary ordered phases, the phase diagrams, and the grain growth dynamics and structural transformation processes, including the emergence of topological defects, are examined. The results are compared to the ordering and assembly of two-component colloidal systems. Two factors governing the binary phase ordering are identified, the coupling and competition between the length scales of two subl…
Employing elastic and inelastic neutron scattering (INS) techniques, we report on detailed microscopic properties of the ferromagnetism in he magnetic topological insulator (Bi$_{0.95}$Mn$_{0.05}$)$_{2}$Te$_{3}$. Neutron diffraction of polycrystalline samples show the ferromagnetic (FM) ordering is long-range within the basal plane, and mainly 2D in character with short-range correlations between layers below $T_{\mathrm{C}} \approx 13$ K. Despite the random distribution of the dliute Mn atoms, we find that the 2D-like magnetic peaks are commensurate with the chemical structure, and the absenc…
We present first principles calculations of the magnetic and orbital properties of Ba$_2$NaOsO$_6$ (BNOO), a 5$d^1$ Mott insulator with strong spin orbit coupling (SOC) in its low temperature emergent quantum phases. Our computational method takes into direct consideration recent NMR results that established that BNOO develops a local octahedral distortion preceding the formation of long range magnetic order. We found that the two-sublattice canted ferromagnetic ground state identified in Lu \etal, Nature Comm. {\bf 8}, 14407 (2017) is accompanied by a two-sublattice staggered orbital ordering…
In the paper a theoretical study of critical (Curie) temperature of diluted ferromagnet based on multilayer graphene (or graphite) with hydrogen adatoms deposited over carbon atoms belonging to single sublattice is presented. The calculations are performed within Pair Approximation (PA) for diluted ferromagnetic system with long-range interactions. The method is able to take into account the spin-space anisotropy of coupling. The results obtained within Mean Field Approximation (MFA) are also presented for comparison. The assumed interaction between hydrogen adatom spins is inversely proportio…
Ambiguity in B-Site cation ordering: A Case study of the double perovskite Ca$_2$CoNbO$_6$
Skolkovo Institute of Science and Technology（斯科尔科沃科学技术研究所）；Zavoisky Physical-Technical Institute, Federal Research Center “Kazan Scientific Center of RAS”（扎沃伊斯基物理技术研究所，俄罗斯科学院鞑靼斯坦科学中心联邦研究中心）；Kazan (Volga Region) Federal University（喀山（伏尔加沿岸）联邦大学）；Institute of Solid State Chemistry of the Russian Academy of Sciences (UB)（俄罗斯科学院固体化学研究所（乌拉伯分支））
Ever-increasing interests to more accurate thermodynamic predictions of phase diagrams motivate more reliable thermodynamic models to be developed. The Modified Quasichemical Model within the two-sublattice Quadruplet Approximation (MQMQA) was thus established in well response to these interests and motivations. However, the model still needs to be further improved in order to have better thermodynamic predictions of arbitrary reciprocal solutions. The present paper proposes a new and generic formalism to characterize the Gibbs energy of the ternary reciprocal quadruplet within the framework o…
We present theoretical studies of morphology, stability, and electronic structure of monolayer hexagonal CBN alloys with rich content of h-BN and carbon concentration not exceeding 50 %. Our studies are based on the bond order type of the valence force field to account for the interactions between atomic constituents and Monte Carlo method with Metropolis algorithm to establish equilibrium distribution of atoms over the lattice. We find out that the phase separation into graphene and h-BN domains occurs in the majority of growth conditions. Only in N-rich growth conditions, it is possible to o…
A pseudospin model for description of the influence of the electric field, confined to the plane of sublattice polarization, on the two-dimensional squaric acid antiferroelectrics is developed. The system behavior is analyzed in terms of the parameters of ferroelectric and antiferroelectric ordering, as well as the non-collinearity angle $θ$, which is the angle between sublattice polarizations. The temperature-electric field $T-E_1$ phase diagram is constructed. Most of the field-induced transitions are found to be associated with polarization rotation. The observed phases include the collinea…
We reveal that the origin of ferromagnetism caused by $sp$ electrons in graphene with vacancies can be traced to electrons partially filling $sp^{2*}$-antibonding and $p_z^*$-nonbonding states, which are induced by the vacancies and appear near the Fermi level. Because the spatial wavefunctions of the both states are composed of atomic orbitals in an antisymmetric configuration, their spin wavefunctions should be symmetric according to the electron exchange antisymmetric principle, leading to electrons partially filling these states in spin polarization. Since this $p_z^*$ state originates not…
