The introduction of the concept of topological insulators (TI) has added anew dimension to our understanding of the nature of the insulating state.These novel insulators differ from the well known ones (sometimes referredto as trivial insulators) such as band insulators, Mott insulators,covalent insulators, Anderson insulators in a fundamental way. All theseinsulators including the TIs have bulk band gaps and surface states whichcan carry current. But in TIs the surface states are topologicallyprotected, gapless and have striking spin texture. The surface stateelectrons possess an intrinsic chirality which enables the propagation ofconduction electrons where spin is locked to momentum and backscatteringevents are suppressed. This remarkable surface electronic structure arisesfrom spin-orbit interaction and time reversal invariance, resulting in theformation of odd number of massless Dirac cones in the single particleenergy dispersion. The charge transport through these topologicallyprotected surface states is dissipationless. After a review of theseexciting features of the TIs I will discuss some recent experimentalobservations (Angle Resolved Photo Emission, Scanning TunnelingMicroscopy, Nuclear Magnetic Resonance etc) and their understanding from atheoretical perspective within single particle electronic structure.
27/08/2012 at 4:00 pm
Niraj Kumar (UCSD, USA)
Condensed Matter Theory Seminar
Lecture Hall Block A, Institute of Physics
Document Date:
Non-equilibrium thermodynamics and efficiency of small systems
Amphiphilic molecules are made up of two parts of opposing nature: one is a hydrophilic part referred to as the ‘head’ group and other is a hydrophobic ‘tail’ group. The non-polar tail part is usually a long hydrocarbon chain which is covalently attached to the polar head group. Depending on physicochemical properties, they form self-assembled structures of various shapes which are highly appreciated in soft matter industry. Interesting liquid crystalline phases observed at low water content in these systems will be discussed along with their possible routeof phase transition. A class of biomolecules also belongs to this group. The talk will include a synchrotron x-ray scattering study of model bio-membrane and its interaction with ions. The study provides unprecedented structural insights into the interaction and promises the physicists to provide high resolution structural details of membrane-macromolecule interaction. The future research with these molecules will also be presented.
