Sushanta Dattagupta

National Institute of Technology Durgapur, India

19 September 2023 Tue 4 pm

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Graphene -- a wonder laboratory -- is a system with remarkable properties and applications. The essential quantum richness of the two-dimensional material that has earned itself the epithet of a Dirac solid, has been described in the literature. It turns out that the basic building blocks of graphene -- from the electronic configuration of a single carbon (C) atom -- to the hybridization of the orbitals of two nearest neighbour C atoms, yielding a honeycomb lattice in the tight-binding limit -- can be used to teach distinct aspects of master's level quantum mechanics, both relativistic and non-relativistic. After giving a pedagogical overview of these basic attributes, I will turn attention to the study of nonlinear optical conductivity of graphene. The optical absorption beyond the linear Drude-Kubo regime is investigated in terms of the familiar spin-boson model of quantum dissipation, in which the 'spin' refers to the two-state system of valence and conduction band wave functions for a given k-value of the momentum. The necessary formalism is based on the 'Rotating Wave Approximation' of Quantum Optics and the 'Master Equation' approach to non-equilibrium statistical mechanics. The different roles of phonons and electrons in inducing quantum dissipation and thereby optical absorption will be analyzed.and the results for spin-lattice and spin-spin relaxation rates will be graphically illustrated.

  1. spin-boson model for nonlinear optical conductivity of graphene