Coherent dynamics in broken symmetry phases

Chatterjee, Abhinava (2019) Coherent dynamics in broken symmetry phases. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Abhinava Chatterjee (14MS098)) 14MS098.pdf - Submitted Version Restricted to Repository staff only Download (999kB)

Abstract

In this thesis, we outline the dynamics of symmetry broken phases particularly related to condensation phenomena. The thesis is primarily divided into parts - in the first part, Kerr frequency combs in the driven nonlinear Schrödinger equation are obtained in the form of a fractional transform, involving sinusoidal functions. This exactly connects the periodic solution space of this non-integrable system with that of the linear harmonic oscillator. The solutions are found in two distinct classes, corresponding to the presence and absence of a background condensate. The latter case is characterized by a unique solution, while the former shows a rich phase space offering parametric control over the frequency space comb. In the second part of the thesis, we study the topological properties of magnon excitations in a S = 1=2 Heisenberg antiferromagnet on a bilayer honeycomb lattice with strong interlayer coupling complemented by layer restricted Dzyaloshinskii-Moriya (DM) interactions. Our goal is to investigate the BEC of field-induced triplon excitations on the ground state. The presence of the DM term in the Hamiltonian introduces a gap in the energy bands. We calculate the topological number associated with the triplon bands and the corresponding effects of the band structure on physical observables.

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