Monopole mining method for high-throughput screening for Weyl semimetals

Abstract

Although topological invariants have been introduced to classify the appearance of protected electronic states at surfaces of insulators, there are no corresponding indexes for Weyl semimetals whose nodal points may appear randomly in the bulk Brillouin Zone (BZ). Here we use a well-known result that every Weyl point acts as a Dirac monopole and generates integer Berry flux to search for the monopoles on rectangular BZ grids that are commonly employed in self-consistent electronic structure calculations. The method resembles data mining technology of computer science and is demonstrated on locating the Weyl points in known Weyl semimetals. It is subsequently used in high throughput screening several hundreds of compounds and predicting a dozen new materials hosting nodal Weyl points and/or lines. PACS numbers:There has been recent surge of interest in topological quantum materials caused by the existence in these systems of robust electronic states insensitive to perturbations [1, 2]. Z 2 invariants have been proposed to detect the protected (quantum Hall-like) surface states in topological insulators (TIs) [3], and, for centrosymmetric crystals, this reduces to finding band parities of electronic wave functions at time-reversal invariant points in the Brillouin zone (BZ) [4]. For a general case, the calculation involves an integration of Berry fields [5], and has been implemented in numerical electronic structure calculations[6] with density functional theory. These methods have allowed for exhaustive searches to identify candidate materials hosting topological insulator phases [7][8][9].Weyl semimetals (WSMs) are closely related systems characterized by a bulk band structure which is fully gapped except at isolated points described by the 2x2 Weyl Hamiltonian [2]. Sometimes these Weyl points extend into lines in the BZ giving rise to nodal line semimetals (NLSMs) [10]. Due to their intriguing properties such as Fermi arc surface states [11], chiral anomaly induced negative magnetoresistance [12], and a semiquantized anomalous Hall effect [13,14], the search for new WSM materials is currently very active. Unfortunately, their identification in infinite space of chemically allowed compounds represents a challenge: there is no corresponding topological index characterizing WSM phase, and the Weyl points may appear randomly in the bulk BZ. General principles, such as broken time reversal or inversion symmetry, or emergence of the WSM phase between topologically trivial and non-trivial insulating phases [11] are too vague to guide their high throughput screening, and recent group theoretical arguments [15,16] to connect crystal symmetry with topological properties still await their practical realization. The progress in this field was mainly serendipitous, although the ideas based on band inversion mechanism [17] or analyzing mirror Chern numbers [18,19] were proven to be useful in FIG. 1: a. A typical cone dispersion relationship E(k)=±v|k − k WP | for the Weyl point plotted within a rectangular area in k-space se...

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Colossal anomalous Nernst effect in a correlated noncentrosymmetric kagome ferromagnet

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