Wednesday, June 13, 2012

1206.2462 (Kasper Duivenvoorden et al.)

On topological phases of spin chains    [PDF]

Kasper Duivenvoorden, Thomas Quella
Topological phases of one-dimensional spin systems with various symmetries have been classified using group cohomology. In this paper, we revisit this problem for general spin chains which are invariant under a continuous on-site symmetry group G. We evaluate the relevant cohomology groups and find that the topological phases are in one-to-one correspondence with the elements of the fundamental group of G if G is compact, simple and connected. For spin chains with symmetry PSU(N)=SU(N)/Z_N our analysis implies the existence of N distinct topological phases. For symmetry groups of orthogonal, symplectic or exceptional type we find up to four different phases. Our work suggests a natural generalization of Haldane's conjecture beyond SU(2).
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