Coexistence of electron and phonon topology in conjunction with quantum transport device modeling.

The escalating research in the field of topology necessitates an understanding of the underlying rich physics behind the materials possessing unique features of non-trivial topology in both electronic and phononic states. Due to the interaction between electronic quasiparticles and spin degrees of freedom, the realization of magnetic topological materials has opened up a new frontier with unusual topological phases, however, these are rarely reported alongside phononic quasiparticle excitations. In this work, by first-principles calculations and symmetry analysis, the intermetallic ferromagnetic compounds MnGaGe and MnZnSb with the coexistence of exceptional topological features in the electronic and phononic states are proposed. These compounds host nodal surface onky=πplane in bulk Brillouin zone in the electronic and phononic spectra protected by the combination of time-reversal symmetry and nonsymmorphic two-fold screw-rotation symmetry. In the former case, a spin-polarized nodal surface is present in the majority and minority spin channels and found to be robust to ground-state magnetic polarization. The presence of nodal line features is analyzed in both the quasiparticle spectra, whose non-trivial nature is confirmed by the Berry phase calculation. The incorporation of spin-orbit coupling in the electron spectra introduces distinctive characteristics in the transport properties, facilitating the emergence of anomalous Hall conductivity through Berry curvature in both bulk and monolayer. Furthermore, the monolayer has been proposed as a two-terminal device model to investigate the quantum transport properties using the non-equilibrium Green's function approach. This superlative combination of observations and modeling sets the path for a greater level of insight into the behavior and aspects of topological materials at the atomic scale.

Evidence for topological features in the electronic and phononic bands of ZGeSb (Z = Hf, Zr, Ti) class of compounds.

Nontrivial topological properties in materials have been found in either the electronic or the phononic bands, but they have seldom been shown in both for a compound. With the aid of first-principle calculations, our paper attempts to find topological features in the electron and phonon band structures of ZGeSb (Z = Hf, Zr, Ti) class of compounds. The electron band structure exhibits two nodal rings in each of these compounds. Furthermore, drumhead surface states (DSS) have also been shown. The phonon band structure depicts one nodal ring in each of these compounds. DSS is also seen in the phonon surface states. Layering possibility has also been explored in HfGeSb, which admits a nodal ring each in its electronic and phononic band structure. Finally, these compounds (bulk and mono-layer) possess Dirac points robust to spin-orbit coupling effects, with at least one such Dirac point with its linear dispersion extending to the Fermi energy. Therefore, these compounds fall under the topological nodal line metals class, which is rarely seen in materials. These compounds' theoretical nontrivial topological nature in their electronic and phononic band structure provides a profound grasp of electronic and phononic nodal-line physics and is a good candidate for experimental verification. The existence of Dirac points close to the Fermi level could also motivate one to look for extreme magnetoresistance in these compounds. Moreover, given their largely metallic nature, these compounds become an excellent arena for novel device applications.