Abstract:A spin-1 2 two-leg ladder with four-spin ring exchange is studied by quantized Berry phases, used as localorder parameters. Reflecting local objects, nontrivial ͑͒ Berry phase is founded on a rung for the rung-singlet phase and on a plaquette for the vector-chiral phase. Since the quantized Berry phase is topologically invariant for gapped systems with the time-reversal symmetry, topologically identical models can be obtained by the adiabatic modification. The rung-singlet phase is adiabatically connected to a… Show more
“…[15] The global Berry phase has been used as a topological index for the Hermitian Hamiltonian. [3,19] Here we find the gauge invariance of the complex Berry phase and global Berry phase for a generic non-Hermitian Hamiltonian and generalize the global Berry phase to identify the topological invariance for non-Hermitian Hamiltonian.…”
Studying the topological invariance and Berry phase in non-Hermitian systems, we give the basic properties of the complex Berry phase and generalize the global Berry phases Q to identify the topological invariance to non-Hermitian models. We find that Q can identify a topological invariance in two kinds of non-Hermitian models, two-level non-Hermitian Hamiltonian and bipartite dissipative model. For the bipartite dissipative model, the abrupt change of the Berry phase in the parameter space reveals quantum phase transition and relates to the exceptional points.These results give the basic relationships between the Berry phase, quantum and topological phase transitions.
“…[15] The global Berry phase has been used as a topological index for the Hermitian Hamiltonian. [3,19] Here we find the gauge invariance of the complex Berry phase and global Berry phase for a generic non-Hermitian Hamiltonian and generalize the global Berry phase to identify the topological invariance for non-Hermitian Hamiltonian.…”
Studying the topological invariance and Berry phase in non-Hermitian systems, we give the basic properties of the complex Berry phase and generalize the global Berry phases Q to identify the topological invariance to non-Hermitian models. We find that Q can identify a topological invariance in two kinds of non-Hermitian models, two-level non-Hermitian Hamiltonian and bipartite dissipative model. For the bipartite dissipative model, the abrupt change of the Berry phase in the parameter space reveals quantum phase transition and relates to the exceptional points.These results give the basic relationships between the Berry phase, quantum and topological phase transitions.
“…19,20 The relevance of the four-spin cyclic exchange has also been reported [21][22][23][24][25][26][27][28][29] in the frame of inelastic neutron-scattering experiments for cuprates such as La 2 CuO 4 , La 6 The model (1) in the N = 2 case has been studied extensively over the years by means of different analytical and numerical approaches. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] The zero-temperature phase diagram is rich and several exotic phases have been identified such as a scalar chirality phase which spontaneously breaks the time-reversal symmetry. 31 When J ⊥ > 0, the ring exchange destabilizes the well-known rung-singlet (RS) phase of the standard two-leg spin ladder and a staggered dimerization (SD) phase emerges.…”
Four-spin exchange interaction has been raising intriguing questions
regarding the exotic phase transitions it induces in two-dimensional quantum
spin systems. In this context, we investigate the effects of a cyclic four-spin
exchange in the quasi-1D limit by considering a general N-leg spin ladder. We
show by means of a low-energy approach that, depending on its sign, this ring
exchange interaction can engender either a staggered or a uniform dimerization
from the conventional phases of spin ladders. The resulting quantum phase
transition is found to be described by the SU(2)_N conformal field theory. This
result, as well as the fractional value of the central charge at the
transition, is further confirmed by a large-scale numerical study performed by
means of Exact Diagonalization and Density Matrix Renormalization Group
approaches for N \le 4
“…Although the plateau phase under consideration can be mapped to the zero magnetization phase in the XXZ chain in the strong rung coupling limit, the fractional quantization is not expected in the XXZ chain since it does not admit the diagonal edge. is induced by a ring exchange [43,48], which is written as [19,20,35,43,49]…”
Section: Symmetry-breaking Boundary and Fractional Quantization Ofmentioning
confidence: 99%
“…The 1/2-plateau phase appears in the applied magnetic field, which breaks most of the symmetry of the system. The ladder model itself has been studied extensively [12][13][14][15][16][17][18] and some of the studies shed light on the topological aspects of the ladder model [19][20][21], but the focus has mainly been on the case without magnetic * kariyado@rhodia.ph.tsukuba.ac.jp † hatsugai@rhodia.ph.tsukuba.ac.jp field. (Very recently, plateau phases at finite magnetization in spin chains have been studied using a SPT viewpoint in Ref.…”
Topological properties of the spin-1/2 dimerized Heisenberg ladder are investigated, focusing on the plateau phase in the magnetic field whose magnetization is half of the saturation value. Although the applied magnetic field removes most of the symmetries of the system, there is a symmetry-protected topological phase supported by the spatial inversion symmetry. The Z 2 Berry phase associated with a symmetry-respecting boundary and quantized into 0 and π is used as a symmetry-protected topological order parameter. Edge states are also analyzed to confirm the bulk-edge correspondence. In addition, a symmetry-breaking boundary is considered. Then, we observe a different type of quantization of the Berry phase, i.e., a quantization into ±π/2 of the Berry phase. In this case, the bulk-edge correspondence is also different, namely, there emerge "polarized" edge states for the case with ±π/2 quantization. We also evaluate the entanglement entropy by the infinite time-evolving block decimation (iTEBD) to complement the Berry-phase-based arguments. Further, a different type of the topological order parameter is extracted from the matrix product state representation of the ground state given by the iTEBD.
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