Recent Advances in Topological Materials

<strong>School of Physical Sciences Jawaharlal Nehru University, New Delhi</strong> <strong>Recent Advances in Topological Materials</strong> <strong>Chandra Sekhar</strong> Max Planck Institute for Chemical Physics of Solids, Dresden <strong>Date: June 24, 2015</strong> Topological materials have newly been identified as quantum materials and their properties are highlighted by topology. These materials are further classified into three groups and these are topological insulator, Dirac semimetal, and Weyl semimetal. Topological insulators (TIs) are insulating in bulk (interior) but metallic (conducting) on the surface or edge. This conducting surface originates from the inversion of bulk bands as a result of strong spin-orbit coupling. Depending on materials, not necessarily bulk is always an insulator; if it is gapless, materials turn into a semimetal. Other two topological materials have semimetallic bulk where valence and conduction bands touch at Fermi level at the same point or different points. Depending on whether the bands are doubly degenerate (same point) or nondegenerate (different points) at the touching point, such topological material is called a topological Dirac semimetal or a topological Weyl semimetal, respectively. Peculiar properties of topological materials indicate the existence of Majorana, Dirac, and Weyl fermions in condensed matter. My talk will focus on different methods of crystal growth and transport properties of topological materials. For example, NbP is a Weyl semimetal that shows extremely large transverse magnetoresistance and mobility that accompanied by strong quantum oscillations. Interestingly, this series of material also show negative longitudinal magnetoresistance which reflects the strong evidence of presence of Weyl fermions.