2014 CAP Congress / Congrès de l'ACP 2014

String order parameters and topological indices in the dimerized XY chain

18 Jun 2014, 19:10

2m

W-132 (Laurentian University / Université Laurentienne)

Poster (Student, In Competition) / Affiche (Étudiant(e), inscrit à la compétition) Condensed Matter and Materials Physics / Physique de la matière condensée et matériaux (DCMMP-DPMCM) DCMMP Poster Session, with beer (4) / Session d'affiches DPMCM, avec bière (4)

Speaker

Mr Toplal Pandey (Department of Physics, Laurentian University)

Description

We study the exactly solvable dimerized antiferromagnetic spin-1/2 XY chain which exhibits quantum phase transitions. We analyze the phase diagram of the model and order parameters in various regions of the parametric space. We utilize the spin duality transformations and standard results of exactly solvable spin chains to analytically calculate the conventional Landau long-range order parameters and non-local topological string order parameters. These order parameters are used to classify different gapped phases. The local and nonlocal order parameters are mutually exclusive in two phases and coexisting in other two phases. The gapped phases can also be characterized by their topological winding number (Pontyagin index). The topological numbers change their integer values while crossing the phase boundaries. We find different topological indices in the two regions of the same gapped phase where the topological numbers change without gap closing. We show that the different topological indices in this phase are associated with level crossing. Thus the change of topological numbers does not always indicate gap closing or quantum phase transition.