arXiv subjects

Augusto L. Araújo

Publications and source records attributed to Augusto L. Araújo.

4 recordsLinked to original sources

arXiv2025

Weyl semimetal engineering by symmetry control in NiTe$_2$

In this work, we investigate the emergence of Weyl points in an inversion symmetry-breaking 1T-NiTe$_2$ system. Through first-principles calculations based on the density functional theory combined with tight-binding methods, we find three distinct sets of Weyl crossings under an appropriate symmetry breaking. The first set, composed of four Weyl points, emerges from the Dirac semimetal. Surprisingly, the other two sets result in additional twenty-four Weyl crossings, depending on the weight of the symmetry breaking. We investigate the topological characteristics of the Weyl semimetals by computing the Weyl chirality, Berry curvature, and the evolution of Wannier charge centers. Additionally, the bulk-boundary correspondence has been shown by computing the Fermi arcs. Our results provide a way for creating and manipulating distinct sets of Weyl points with appropriate external control, which can be valuable for applications in Weyltronics.

cond-mat.mtrl-sci↗

arXiv2024

Reentrant topological phase in half-Heusler compounds

Half-Heusler compounds are known for their various compositions and multifunctional properties including topological phases. In this study, we investigate the topological classification of this class of materials based on the ordering of the $Γ_6$, $Γ_8$ states, and a previously overlooked $Γ_6^*$ state, during an adiabatic expansion process. Using first-principles calculations based on density functional theory, we observed that the non-trivial topology is governed by a three-band mechanism. We provide a simple model derived from $k\cdot p$ Hamiltonian that interprets the topological phase in half-Heusler systems. Additionally, we explore the robustness of the topological phase under tension and a new perspective on the topological nature of half-Heusler compounds.

cond-mat.mtrl-sci↗

arXiv2024

DFT2kp: effective kp models from ab-initio data

The $\mathbf{k}\cdot\mathbf{p}$ method, combined with group theory, is an efficient approach to obtain the low energy effective Hamiltonians of crystalline materials. Although the Hamiltonian coefficients are written as matrix elements of the generalized momentum operator $\mathbfπ=\mathbf{p}+\mathbf{p}_{\rm SOC}$ (including spin-orbit coupling corrections), their numerical values must be determined from outside sources, such as experiments or ab initio methods. Here, we develop a code to explicitly calculate the Kane (linear in crystal momentum) and Luttinger (quadratic in crystal momentum) parameters of $\mathbf{k}\cdot\mathbf{p}$ effective Hamiltonians directly from ab initio wavefunctions provided by Quantum ESPRESSO. Additionally, the code analyzes the symmetry transformations of the wavefunctions to optimize the final Hamiltonian. This is an optional step in the code, where it numerically finds the unitary transformation $U$ that rotates the basis towards an optimal symmetry-adapted representation informed by the user. Throughout the paper, we present the methodology in detail and illustrate the capabilities of the code applying it to a selection of relevant materials. Particularly, we show a "hands-on" example of how to run the code for graphene (with and without spin-orbit coupling). The code is open source and available at https://gitlab.com/dft2kp/dft2kp.

cond-mat.mes-hall↗

arXiv2016

Topological Nonsymmorphic Ribbons out of Symmorphic Bulk

States of matter with nontrivial topology have been classified by their bulk symmetry properties. However, by cutting the topological insulator into ribbons, the symmetry of the system is reduced. By constructing effective Hamiltonians containing the proper symmetry of the ribbon, we find that the nature of topological states is dependent on the reduced symmetry of the ribbon and the appropriate boundary conditions. We apply our model to the recently discovered two-dimensional topological crystalline insulators composed by IV-VI monolayers, where we verify that the edge terminations play a major role on the Dirac crossings. Particularly, we find that some bulk cuts lead to nonsymmorphic ribbons, even though the bulk material is symmorphic. The nonsymmorphism yields a new topological protection, where the Dirac cone is preserved for arbitrary ribbon width. The effective Hamiltonians are in good agreement with ab initio calculations.

cond-mat.mes-hall↗