Groundstate factorization and quantum phase transition in spin chains

by Prof. Gian Luca Giorgi (IFISC (UIBCSIC) Instituto de Física Interdisciplinar y Sistemas Complejos, Campus Universitat de les Illes Balears, E07122 Palma de Mallorca, Spain)

Wednesday 24 Jun 2009, 17:00 → 19:00 Europe/Rome

Aula 7 (Dipartimento di Fisica - E. E.Fermi)

I will discuss the problem of ground state factorization in spin chains. After a general introduction about the topic, I will describe in detail the case of the XY chain in a transverse field. It will be shown that the factorized ground state is an accidental degeneracy of the Hamiltonian. A finitesize analysis allows one to establish the cause of the existence of different regimes in the symmetrybroken phase and to emphasize the role of the factorizing field in the process. In the second part of the seminar, I will extend the study to dimerized chains, where, together with the usual ferromagnetic and antiferromagnetic regimes, a third case emerges, consisting of an antiferromagnetic Neéltype ground state whose unitary cell is represented by a pairs of spins. As in the regular XY model, the factorizing field represents a border line between region exhibiting different symmetrybreaking mechanisms