Paper detail

New gapped quantum phases for S=1 spin chain with D2h symmetry

We study different quantum phases in integer spin systems with on-site D2h=D2xZ2 and translation symmetry. We find four distinct non-trivial phases in S=1 spin chains despite they all have the same symmetry. All the four phases have gapped bulk excitations, doubly-degenerate end states and the doubly-degenerate entanglement spectrum. These non-trivial phases are examples of symmetry protected topological (SPT) phases introduced by Gu and Wen. One of the SPT phase correspond to the Haldane phase and the other three are new. These four SPT phases can be distinguished experimentally by their different response of the end states to weak external magnetic fields. According to Chen-Gu-Wen classification, the D2h symmetric spin chain can have totally 64 SPT phases that do not break any symmetry. Here we constructed seven nontrivial phases from the seven classes of nontrivial projective representations of D2h group. Four of these are found in S=1 spin chains and studied in this paper, and the other three may be realized in S=1 spin ladders or S=2 models.