In a recent paper, Ibanez-Azpiroz et al. [Phys. Rev. B 97, 245143 (2018)] derive a band-truncation-error-free formula for calculating the generalized derivative of the interband dipole matrix using Wannier interpolation. In practice, the denominators involving intermediate states are regularized by introducing a finite broadening parameter. In this Comment, I show that when a finite broadening parameter is used, a correction term must be added to the generalized derivative to obtain results that are independent of the phase convention for the Bloch sums.

There has been interest in the spin transport properties of the Aubry-Andre-Harper model at high temperatures under weak integrability breaking, in particular for small interactions or small fields. We present results that show that the model is diffusive, meaning that the claimed superdiffusion is a finite-size effect.

We report the crystal structure and magnetic behavior of the 4d(3) spin-3/2 silicophosphate MoP3SiO11 studied by high-resolution synchrotron x-ray diffraction, neutron diffraction, thermodynamic measurements, and ab initio band-structure calculations. Our data revise the crystallographic symmetry of this compound and establish its rhombohedral space group (R (3) over barc) along with the geometrically perfect honeycomb lattice of the Mo3+ ions residing in disconnected MoO6 octahedra. Long-range antiferromagnetic order with the propagation vector k = 0 observed below T-N = 6.8 K is a combined effect of the nearest-neighbor in-plane exchange coupling J similar or equal to 2.6 K, easy-plane single-ion anisotropy D similar or equal to 2.2 K, and a weak interlayer coupling J(c) similar or equal to 0.8 K. The 12% reduction in the ordered magnetic moment of the Mo3+ ions and the magnon gap of Delta similar or equal to 7 K induced by the single-ion anisotropy further illustrate the impact of spin-orbit coupling on the magnetism. Our analysis puts forward single-ion anisotropy as an important ingredient of 4d(3) honeycomb antiferromagnets despite their nominally quenched orbital moment.

In this paper we present an algorithm which allows single-stage direct Langevin dynamics simulations of the escape rate over arbitrarily high energy barriers employing the concept of the energy-dependent temperature (EDT). In our algorithm, simulation time required for the computation of the escape rate does not increase with the energy barrier. This is achieved by using in simulations an effective temperature which depends on the system energy: around the energy minima this temperature is high, whereas it tends towards room temperature when the energy approaches the saddle point value. Switching times computed via our EDT algorithm show an excellent agreement with results obtained with the established forward flux sampling (FFS) method. As the simulation time required by our method does not increase with the energy barrier, we achieve a very large speedup when compared even to our highly optimized FFS version with interfaces placed equidistantly in the energy space. In addition, our method does not suffer from stability problems occurring in multistage algorithms (like FFS and energy bounce methods) due to the multiplication of a large number of transition probabilities between the interfaces.

Nd-based pyrochlore oxides of the form Nd2B2O7 have garnered a significant amount of interest owing to the moment fragmentation physics observed in Nd2Zr2O7 and speculated in Nd2Hf2O7. Notably this phenomenon is not ubiquitous in this family, as it is absent in Nd2Sn2O7, which features a smaller ionic radius on the B site. Here, we explore the necessary conditions for moment fragmentation in the Nd pyrochlore family through a detailed study of the mixed B-site pyrochlore Nd2GaSbO7. The B site of this system is characterized by significant disorder and an extremely small average ionic radius. Similarly to Nd2Sn2O7, we find no evidence for moment fragmentation through our bulk characterization and neutron scattering experiments, indicating that chemical pressure (and not necessarily the B-site disorder) plays a key role in the presence or absence of this phenomenon in this material family. Surprisingly, the presence of significant B-site disorder in Nd2GaSbO7 does not generate a spin-glass ground state and instead the same all-in-all-out magnetic order identified in other Nd pyrochlores is found here.