Entanglement signature of fully and partially dimerized phases in frustrated spin chains

• URL: http://arxiv.org/abs/2605.02581v1
• Date: Mon, 04 May 2026 13:34:00 GMT
• Title: Entanglement signature of fully and partially dimerized phases in frustrated spin chains
• Abstract summary: entanglement entropy of exact valence-bond ground states is studied in two frustrated one-dimensional spin chains.<n>The entropy saturates to a finite constant in the thermodynamic limit, confirming area-law behavior.<n>The MG model and FD phase exhibit similar entanglement behavior, differing primarily in saturation magnitude determined by spin value and bond multiplicity.<n>The PD phase shows qualitatively distinct signatures, including multiple half-chain saturation values depending on the bond type at the cut.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: The von Neumann entanglement entropy of exact valence-bond ground states is studied in two frustrated one-dimensional spin chains: the spin-1/2 Majumdar-Ghosh (MG) model and the spin-3/2 J1-J2-J3 chain in its fully dimerized (FD) and partially dimerized (PD) phases. Using matrix-product-state representations, the entropy is computed as a function of system size for three complementary bipartitions - half-chain, single-site, and pairwise - under both open and periodic boundary conditions. In all cases, the entropy saturates to a finite constant in the thermodynamic limit, confirming area-law behavior. The saturation values, extracted via finite-size scaling, are directly related to the underlying virtual-spin bond structure. The MG model and FD phase exhibit similar entanglement behavior, differing primarily in saturation magnitude determined by spin value and bond multiplicity, and both display even-odd oscillations and exponential convergence with system size. In contrast, the PD phase shows qualitatively distinct signatures, including multiple half-chain saturation values depending on the bond type at the cut, asymmetric edge contributions in the single-site entropy, and a multi-band structure in the pairwise entropy reflecting the coexistence of single- and double-singlet bonds. These results establish entanglement entropy as a robust signature of frustrated bond architecture, enabling clear distinction among dimerized phases with different spin magnitude, bond multiplicity, and dimerization patterns.

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