Understanding the mechanism of interactions inside the crystalline solids through electronic structure analysis and, thereby, tuning the properties of materials has been at the forefront of materials research. Herein, with the aid of density functional theory (DFT) calculations and parametric tight-binding (TB) modeling, in this talk, we will discuss spin-orbit coupling (SOC) and symmetry-breaking effects in halide perovskites (HPs), halide double perovskites (HDPs), and transition metal dichalcogenides (TMDs) through the investigating electronic structure properties. Furthermore, we will present tailoring of the functionality in these materials either by altering the crystal symmetry or with suitable defect engineering techniques.



In the first part of the talk, we focus on developing model Hamiltonians for the family of HPs and HDPs. We present a comprehensive electronic structure study on the perovskites ABX$_3$ (centrosymmetric and non-centrosymmetric) and establish a minimal basis set based effective model Hamiltonians, which accurately reproduce bulk and surface electronic structures in the vicinity of Fermi level. We explore the impact of SOC on non-centrosymmetric HPs, revealing the emergence of the Rashba effect and spin textures that depend on the polarization field. We further investigate the tuning of optoelectronic properties on HDPs.



The second part focuses on state-of-the-art defect engineering techniques to realize novel quantum phases in TMDs. We show that the chain-doped monolayer TMDs MX$_2$/M$^\prime$ exhibit one-dimensional (1D) bands when a higher-valence transition-metal element M$^\prime$ replaces M atoms on a single zigzag chain. These 1D bands, occurring in the fundamental gap of the pristine material, are dispersive along the doped chain but are strongly confined along the lateral direction. This confinement could show novel 1D physics, including a new type of Tomonaga-Luttinger liquid behavior, multi-orbital Mott insulator physics, and an unusual band widening. Furthermore, we study the orbital and spin polarization near magnetic impurities in metallic TMDs such as 2H-NbSe$_2$. Magnetic impurity induces the standard spin polarization in its neighborhood and a sizable orbital (valley) polarization, both with the characteristic Friedel oscillations.