The NQPI Seminar Series features graduate student Miguel Abraham Mojarro Ramirez discussing "Strain-induced topological phase transitions in kagome lattices" on April 20 from 4:10 to 5:15 p.m. in Clippinger 194.

Abstract: Topological kagome magnets and superconductors are an ideal playground for the study of topological phases and correlated phenomena due to the simultaneous presence of Dirac fermions, flat bands and van-Hove singularities, as revealed by the recent realization of several kagome materials. In this work, we study the effects of a uniform strain on the electronic and topological properties of the 2D kagome lattice using a tight-binding formalism that includes intrinsic and Rashba spin-orbit coupling (SOC). The degeneracy at the Γ point, where a flat-band-parabolic-band touching occurs, evolves into a pair of (tilted) type-I Dirac cones owing to a uniform strain, as shown by effective Hamiltonians, where the anisotropy and tilting of the bands depend in a nontrivial way on the magnitude and direction of the strain field. Interestingly, we find that the Dirac cones become type-III (including flat dispersions) when the strain is applied along the bonds of the lattice. As expected, the inclusion of intrinsic SOC opens a gap at the emergent Dirac points, making the strained flat band to become topological, as characterized by a nontrivial Z₂ index. We show that the strain drives the systems into a trivial or topological phase for strains of a few percent, allowing topological transitions via uniform deformations. Additionally, when the Rashba interaction is included, semimetallic phases appear in the topological phase diagrams. These findings suggest an alternative way of engineering anisotropic tilted Dirac bands with tunable topological properties in strained kagome lattices.