Realising square and diamond lattice $S=1/2$ Heisenberg antiferromagnet models in the $α$ and $β$ phases of the coordination framework, KTi(C$_2$O$_4$)$_2\cdot$\textit{x}H$_2$O

KTi（SO4）2的电子结构。H2O - a S=1/2阻挫链反铁磁体

Electronic structure of KTi(SO4)2.H2O - a S=1/2 frustrated chain antiferromagnet

化合物KTi（SO 4）2·H2O最近被报道为准一维自旋1/2化合物，沿着链具有竞争的反铁磁最近邻交换J1和次最近邻交换J2，阻挫比α = J2/J1 ~ 0.29 [Chem.Mater.第20卷，第8页（2008）]。在这里，我们报告了一个基于微观的磁性模型，该化合物来自密度泛函电子结构计算以及各自的紧束缚模型。我们的计算证实了系统的准一维性质与反铁磁J1和J2，但建议一个显着更大的挫折比α ~ 1.1 +-0.2。基于转移矩阵重整化群计算，我们发现，由于J1-J2模型的内在对称性，我们得到的较大的阻挫比α也与以前的热力学数据一致。为了解决这个问题，我们建议进行高场磁化测量和低温磁化率测量，这应该可以精确地识别挫折比α。

Realising the Symmetry-Protected Haldane Phase in Fermi-Hubbard Ladders

Topology in quantum many-body systems has profoundly changed our understanding of quantum phases of matter. The paradigmatic model that has played an instrumental role in elucidating these effects is the antiferromagnetic spin-1 Haldane chain. Its ground state is a disordered state, with symmetry-protected fourfold-degenerate edge states due to fractional spin excitations. In the bulk, it is characterised by vanishing two-point spin correlations, gapped excitations, and a characteristic non-local order parameter. More recently it was understood that the Haldane chain forms a specific example o…

Kitaev interactions in the Co honeycomb antiferromagnets Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$

Co$^{2+}$ ions in an octahedral crystal field, stabilise a j$_{eff}$ = 1/2 ground state with an orbital degree of freedom and have been recently put forward for realising Kitaev interactions, a prediction we have tested by investigating spin dynamics in two cobalt honeycomb lattice compounds, Na$_2$Co$_2$TeO$_6$ and Na$_3$Co$_2$SbO$_6$, using inelastic neutron scattering. We used linear spin wave theory to show that the magnetic spectra can be reproduced with a spin Hamiltonian including a dominant Kitaev nearest-neighbour interaction, weaker Heisenberg interactions up to the third neighbour a…

通过调节FeSe1-xSx超导体的向列性和磁性使Tc最大化

Maximizing Tc by tuning nematicity and magnetism in FeSe1-xSx superconductors

铁基超导电性的一个基本问题是电子向列性和磁性在实现高转变温度（$T_{\rm c}$）中的作用。为了解决这个问题，FeSe是一种关键材料，因为它表现出独特的压力相图，包括铁磁有序相和压力诱导的反铁磁有序相。然而，由于FeSe中的这两个相彼此重叠，两个阶对超导电性的影响仍然令人困惑。在这里，我们构建的三维电子相图，温度（$T$）对压力（$P$）和等价的S-取代（$x$），FeSe $_{1-x}$ S $_{x}$，在其中，我们实现了完全分离的铁磁和反铁磁相。在这两者之间，出现了一个扩展的四氢呋喃相，我们发现$T_{\rm c}$的显著增强。完整的相图揭示了两个超导圆顶，在圆顶形反铁磁相的两端具有相似的高$T_{\rm c}$。$T_{\rm c}(P,x)$的变化意味着，除非伴随着磁性的涨落是不相关的高$T_{\rm c}$超导在这个系统中。

Non-collinear magnetism in the post-perovskite thiocyanate frameworks CsM(NCS)$_3$

AMX$_3$ compounds are structurally diverse, a notable example being the post-perovskite structure which adopts a two-dimensional framework with corner- and edge-sharing octahedra. Few molecular post-perovskites are known and of these, none have reported magnetic structures. Here we report the synthesis, structure and magnetic properties of molecular post-perovskites: CsNi(NCS)$_3$, a thiocyanate framework, and two new isostructural analogues CsCo(NCS)$_3$ and CsMn(NCS)$_3$. Magnetisation measurements show that all three compounds undergo magnetic order. CsNi(NCS)$_3$ (Curie temperature, $T_\ma…

β-Mn：复杂结构中涌现的简单性

β-Mn: Emergent Simplicity in a Complex Structure

研究了金属阻挫磁体β-MnCo中的低温自旋关联。单晶极化中子散射实验揭示了T=0.05 K时高结构磁散射的持续性和周期磁序的缺失。我们采用反向蒙特卡罗精化和平均场论模拟来构造一个简单的有效哈密顿量，它占磁散射。我们确定的相互作用描述了一个新兴的自旋结构，模仿三角晶格反铁磁体。在复杂的晶体结构中观察到一个简单的集体磁态是令人惊讶的，因为它扭转了简单晶格上多体相互作用产生的复杂涌现态的既定范式。我们认为，结构的复杂性可能会提供一种途径，实现相关的量子物质的新状态。