Research Projects

Recently, the transition-metal monoslicides, MSi (M=Mn, Fe, Co, Rh) are found to show very interesting physical, magnetic, and electronic properties. Among them, MnSi is found to show a peculiar magnetic structure called the chiral-spin structure leading to the skyrmion lattice. On the other hand, the non-magnetic CoSi and RhSi are found to show topological multifold degenerate band crossing points (BCPs) in the form of bulk quasi-particles in the vicinity of the Fermi level as observed from the electronic band structure. Also, in CoSi and RhSi, there exist surface Fermi arcs connecting the bulk BCPs. Out of the listed interesting physical properties of these systems, we are attracted by the presence of topological multifold degenerate fermions, particularly, in CoSi and RhSi systems due to their potential applications in topological quantum computations. Especially, these multifold BCPs are formed in the presence of inversion symmetry breaking. On the other hand, our recent study on FeSi, using DFT calculation, suggests that the spin-orbit coupling in FeSi partly lifts the degeneracy of the band crossing points. Motivated by this very interesting observation, we would like to perform systematic studies on physical properties and electronic structure of these systems under the time-reversal symmetry breaking. Here the starting materials would be the topological nonmagnetic semimetals CoSi and RhSi. We then start doping these systems by the magnetic elements such as Fe, Cr, Ni, and Mn so that the time-reversal symmetry gets broken. We perform the studies on single crystals grown by the Bridgman furnace. As grown single crystals will be characterized structurally and chemically using the X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX). Transport and magnetotransport studies will be performed using physical property measurements set-up. Further vibrating scanning microscopy (VSM) technique will be used to understand the magnetic properties of the doped systems as a function of the sample temperature. Finally, systematic angle-resolved photoemission spectroscopy studies will be performed to unravel the effect of magnetic impurity doping on the degeneracy of the multifold band crossing points in topological semimetals, CoSi and RhSi. Further, we should be able to understand the evolution of surface Fermi arcs with magnetic ion doping using ARPES. Such changes of topological Fermi arcs should be reflected in the magnetoresistance measurements and in the ARPES studies. Thus, our studies not only focus on understanding the physical and electronic properties of the bulk multiband BCPs as a function of magnetic impurity doping but also the associated surface Fermi arcs.