Engineering quantum anomalous Hall phases with orbital and spin degrees of freedom

Combining tight-binding models and first principles calculations, we investigate the quantum anomalous Hall (QAH) effect induced by intrinsic spin-orbit coupling (SOC) in buckled honeycomb lattice with sp orbitals in an external exchange field. Detailed analysis reveals that nontrivial topological properties can arise utilizing not only spin but also orbital degrees of freedom in the strong SOC limit, when the bands acquire non-zero Chern numbers upon undergoing the so-called orbital purification. As a prototype of a buckled honeycomb lattice with strong SOC we choose the Bi(111) bilayer, analyzing its topological properties in detail. In particular, we show the emergence of several QAH phases upon spin exchange of the Chern numbers as a function of SOC strength and magnitude of the exchange field. Interestingly, we observe that in one of such phases, namely, in the quantum spin Chern insulator phase, the quantized charge and spin Hall conductivities co-exist. We consider the possibility of tuning the SOC strength in Bi bilayer via alloying with isoelectronic Sb, and speculate that exotic properties could be expected in such an alloyed system owing to the competition of the topological properties of its constituents. Finally, we demonstrate that 3d dopants can be used to induce a sizeable exchange field in Bi(111) bilayer, resulting in non-trivial Chern insulator properties

Rigidity of interfaces in the Falicov-Kimball model

We analyze the thermodynamic properties of interfaces in the three-dimensional Falicov Kimball model, which can be viewed as a primitive quantum lattice model of crystalline matter. In the strong coupling limit, the ionic subsystem of this model is governed by the Hamiltonian of an effective classical spin model whose leading part is the Ising Hamiltonian. We prove that the 100 interface in this model, at half-filling, is rigid, as in the three-dimensional Ising model. However, despite the above similarities with the Ising model, the thermodynamic properties of its 111 interface are very different. We prove that even though this interface is expected to be unstable for the Ising model, it is stable for the Falicov Kimball model at sufficiently low temperatures. This rigidity results from a phenomenon of "ground state selection" and is a consequence of the Fermi statistics of the electrons in the model.Comment: 79 pages, 9 figures included as ps-files, appendix added in revisio

Using restorative justice to rethink the temporality of transition in Chile

Assumptions of linear progress and a clean break with the past have long characterised transitional justice interventions. This notion of temporality has increasingly been problematised in transitional justice scholarship and practice. Scholars have argued that a more complex understanding of temporalities is needed that better accommodates the temporal messiness and complexity of transitions, including their ongoingness, multilayeredness and multidirectionality. Existing critiques, however, have not yet resulted in a new conceptual framework for thinking about transitional temporalities. This article builds on insights from the field of restorative justice to develop such a framework. This framework foregrounds longer timelines, multilayered temporalities and temporal ecologies to better reflect reality on the ground and victims’ lived experiences. We argue that restorative justice is a useful starting point to develop such a temporal framework because of its actor-oriented, flexible and interactive nature and proximity to the field of transitional justice. Throughout this article we use the case of Chile to illustrate some of the complex temporal dynamics of transition and to illustrate what a more context-sensitive temporal lens could mean for such cases of un/finished transition