Executive Summary : | The principal investigation focuses on the realization of exotic topological phases in the recently predicted topological materials of the CoSi family, consisting of CoSi, CoGe, RhSi, and RhGe. These materials are known for hosting exotic chiral fermions with large topological charges and double Weyl fermions. RhSi, another member of the same family, also has a chiral double sixfold degenerate spin-1 Weyl node. The study aims to explore a range of such systems within and beyond the CoSi family through single crystalline synthesis, magneto-transport, magnetic studies, and ARPES. Furthermore, the study aims to study the transformation of electronic structures across different types of exoticness. A doping study of Co1-xRhxSi would reveal a transformation from the exotic properties of CoSi to those in RhSi, displaying the largest possible momentum separation of compensative chiral fermions, the largest proposed topologically nontrivial energy window, and the longest possible Fermi arcs on its surface. The study also seeks to search for signatures of quantum criticality within these transformations, as they are driven by non-thermal control parameters and should be subjected to quantum critical effects. The research also aims to explore the effects of non-transition metal elements like Al on transition metal ions and Group IV elements from the family. The recent theoretical prediction of 25% and 50% doping (by Ge and Sn) at the Si site generates a Weyl semimetallic state out of a multifold fermionic state in CoSi, creating ample prospects for experimental investigation. |