The Distinctiveness of Topological Systems: A Concise Exploration of Topological Insulator and Semimetal

In this presentation, we have briefly discussed topological insulators and semimetals. We observed a metal-semiconductor phase transition for the case of a doped topological insulator. This transition originated from the bulk band, whereas the surface state, which is protected by time-reversal symmetry, remained intact even at room temperature. The distinct surface band observed up to room temperature from the T-dependent ARPES study. However, despite the fact that it is an insulating phase, the bulk band is extremely sensitive to doping. A shift from p-type to n-type in the bulk band can occur if there is a fluctuation in the dopant or if a defect is introduced while the crystal is growing. From the results of the photon energy-dependent ARPES analysis in a nodal line semimetal, we have also seen a robust Dirac cone, which is protected by time reversal and crystalline symmetry. This observation was made in the bulk band of the nodal line semimetal. The discovered Dirac cone has a nature of type II and is safeguarded by C 4 symmetry. The nodal line semimetal demonstrates a number of fascinating properties as well, including the phase transition from semiconductor to metal when a magnetic field is applied to it, along with a very high magneto resistance that is accompanied by carrier compensation. In addition, we visualize the three-dimensional topology of the Fermi surface from the quantum oscillation study and derive several essential parameters, such as effective mass and quantum mobility. Our comprehensive analysis elucidates the intriguing electronic features of topological insulators and nodal line semimetals, highlighting their distinct phenomena deeply anchored in fundamental physics.