(searched for: doi:10.1038/s41524-021-00498-5)
Nature Reviews Physics, Volume 3, pp 283-297; https://doi.org/10.1038/s42254-021-00292-8
Discoveries of topological states and topological materials have reshaped our understanding of physics and materials over the past 15 years. First-principles calculations have had an important role in bridging the theory of topology and experiments by predicting realistic topological materials. In this Review, we offer an overview of the first-principles methodology on topological quantum materials. First, we unify different concepts of topological states in the same band inversion scenario. We then discuss the topology using first-principles band structures and newly established topological materials databases. We stress challenges in characterizing symmetry-independent Weyl semimetals and calculating topological surface states, closing with an outlook on the exciting transport and optical phenomena induced by the topology. First-principles calculations have been very successful in predicting topological quantum materials. This Technical Review covers topological band theory and provides a guide to the study of topological materials with first-principles methods.
Physical Review B, Volume 103; https://doi.org/10.1103/physrevb.103.l121101
We study a class of topological materials which in their momentum-space band structure exhibit threefold degeneracies known as triple points. Focusing specifically on PT-symmetric crystalline solids with negligible spin-orbit coupling, we find that such triple points can be stabilized by little groups containing a three-, four-, or sixfold rotation axis, and we develop a classification of all possible triple points as type A vs type B according to the absence vs presence of attached nodal-line arcs. Furthermore, by employing the recently discovered non-Abelian band topology, we argue that a rotation-symmetry-breaking strain transforms type-A triple points into multiband nodal links. Although multiband nodal-line compositions were previously theoretically conceived and related to topological monopole charges, a practical condensed-matter platform for their manipulation and inspection has hitherto been missing. By reviewing the known triple-point materials with weak spin-orbit coupling and by performing first-principles calculations to predict new ones, we identify suitable candidates for the realization of multiband nodal links in applied strain. In particular, we report that an ideal compound to study this phenomenon is Li2NaN, in which the conversion of triple points to multiband nodal links facilitates a largely tunable density of states and optical conductivity with doping and strain, respectively.
Physical Review B, Volume 103; https://doi.org/10.1103/physrevb.103.054204
Based on the exact muffin-tin orbitals (EMTOs), we developed a first-principles method to calculate the current operators and investigated the anomalous Hall effect in bcc Fe as an example, with which we successfully separated the skew scattering contribution from the side jump and intrinsic contributions by fitting the scaling law with the introduction of sparse impurities. By investigating the temperature dependence of the anomalous Hall effect in bulk Fe, we predicted a fluctuated anomalous Hall angle as a function of temperature when considering only phonons, which, in the future, can be measured in experiments by suppressing magnon excitation, e.g., by applying a high external magnetic field.