models, the AKLT point is not a disorder point: It occurs entirely within an incommensurate phase yet the wave vector remains singular on both sides of the AKLT point. We conjecture that this possibility is generic for models where the representation is not self-conjugate and the transfer matrix non-Hermitian, while for self-conjugate representations the AKLT points remain disorder points.

DOI: 10.1103/physrevb.111.l161118

Related papers

Singularity with and without disorder at AKLT points

Loïc Herviou, Rey, Anthony, Frédéric Mila

The Affleck-Kennedy-Lieb-Tasaki (AKLT) point of the bilinear-biquadratic spin-1 chain is a cornerstone example of a disorder point where short-range correlations become incommensurate, and correlation lengths and momenta are non-analytic. While the presence of singularities appears to be generic for AKLT points, we show that for a family of SU(N) models, the AKLT point is not a disorder point: It occurs entirely within an incommensurate phase yet the wave vector remains singular on both sides of the AKLT point. We conjecture that this new possibility is generic for models where the representation is not self-conjugate and the transfer matrix non-Hermitian, while for self-conjugate representations the AKLT points remain disorder points.The Affleck-Kennedy-Lieb-Tasaki (AKLT) point of the bilinear-biquadratic spin-1 chain is a cornerstone example of a disorder point where short-range correlations become incommensurate, and correlation lengths and momenta are non-analytic. While the presence of singularities appears to be generic for AKLT points, we show that for a family of SU(N) models, the AKLT point is not a disorder point: It occurs entirely within an incommensurate phase yet the wave vector remains singular on both sides of the AKLT point. We conjecture that this new possibility is generic for models where the representation is not self-conjugate and the transfer matrix non-Hermitian, while for self-conjugate representations the AKLT points remain disorder points.

arXiv:2411.17848Nov 26, 20240 citations

Phase transitions of a two-dimensional deformed Affleck-Kennedy-Lieb-Tasaki model

Nicholas Pomata, Ching-Yu Huang, Tzu-Chieh Wei

We study spin-2 deformed-AKLT models on the square lattice, specifically a two-parameter family of $O(2)$ -symmetric ground-state wave functions as defined by Niggemann, Kl\"umper, and Zittartz, who found previously that the phase diagram consists of a N\'eel-ordered phase and a disordered phase which contains the AKLT point. Using tensor-network methods, we not only confirm the N\'eel phase but also find an XY phase with quasi-long-range order and a region adjacent to it, within the AKLT phase, with very large correlation length, and investigate the consequences of a perfectly factorizable point at the corner of that phase.We study spin-2 deformed-AKLT models on the square lattice, specifically a two-parameter family of $O(2)$-symmetric ground-state wave functions as defined by Niggemann, Kl\"umper, and Zittartz, who found previously that the phase diagram consists of a N\'eel-ordered phase and a disordered phase which contains the AKLT point. Using tensor-network methods, we not only confirm the N\'eel phase but also find an XY phase with quasi-long-range order and a region adjacent to it, within the AKLT phase, with very large correlation length, and investigate the consequences of a perfectly factorizable point at the corner of that phase.

arXiv:1711.00036Physical review. B./Physical review. BJul 27, 20186 citations

Path integral for spin-1 chain in the fluctuating matrix product state basis

Jintae Kim, Rajarshi Pal, Jin-Hong Park +1 more

An alternative method of writing down the path integral for spin-1 Heisenberg antiferromagnetic chain is introduced. In place of the conventional coherent-state basis that leads to the nonlinear $\ensuremath{\sigma}$ model, we use a basis called the fluctuating matrix product states which embodies intersite entanglement from the outset. It forms an overcomplete set spanning the entire Hilbert space of the spin-1 chain. Saddle-point analysis performed for the bilinear-biquadratic spin model predicts the Affleck-Kennedy-Lieb-Tasaki (AKLT) state as the ground state in the vicinity of the AKLT Hamiltonian. Quadratic effective action derived by gradient expansion around the saddle point is free from constraints that plagued the nonlinear $\ensuremath{\sigma}$ model and exactly solvable. The obtained excitation modes agree precisely with the single-mode approximation result for the AKLT Hamiltonian. Excitation spectra for other bilinear-biquadratic Hamiltonians are obtained as well by diagonalizing the quadratic action.An alternative method of writing down the path integral for spin-1 Heisenberg antiferromagnetic chain is introduced. In place of the conventional coherent-state basis that leads to the nonlinear $\ensuremath{\sigma}$ model, we use a basis called the fluctuating matrix product states which embodies intersite entanglement from the outset. It forms an overcomplete set spanning the entire Hilbert space of the spin-1 chain. Saddle-point analysis performed for the bilinear-biquadratic spin model predicts the Affleck-Kennedy-Lieb-Tasaki (AKLT) state as the ground state in the vicinity of the AKLT Hamiltonian. Quadratic effective action derived by gradient expansion around the saddle point is free from constraints that plagued the nonlinear $\ensuremath{\sigma}$ model and exactly solvable. The obtained excitation modes agree precisely with the single-mode approximation result for the AKLT Hamiltonian. Excitation spectra for other bilinear-biquadratic Hamiltonians are obtained as well by diagonalizing the quadratic action.

arXiv:2002.11924Physical review. B./Physical review. BJul 6, 20201 citation

Kitaev meets Affleck-Kennedy-Lieb-Tasaki: Competing quantum disorder in spin-3/2 honeycomb systems

Sogen Ikegami, Kiyu Fukui, Rico Pohle +1 more

We investigate an S=3/2 quantum spin model on a two-dimensional honeycomb lattice that continuously interpolates between two paradigmatic quantum disordered states with distinct entanglement structures: the Kitaev quantum spin liquid and the Affleck-Kennedy-Lieb-Tasaki (AKLT) valence bond solid. Combining classical, semi-classical, and exact diagonalization approaches, we map out the ground-state phase diagram and elucidate the role of quantum fluctuations across the entire parameter range. While classical and semi-classical frameworks predict noncoplanar orders competing with a collinear Néel state, we find these phases to be fragile: once full quantum fluctuations are included, they melt into a quantum-entangled state characterized by suppressed spin correlations and enhanced entanglement entropy. Our findings highlight how competition between qualitatively different quantum disordered phases provides a fertile playground for unconventional phases emerging from their interplay and quantum fluctuations.We investigate an S=3/2 quantum spin model on a two-dimensional honeycomb lattice that continuously interpolates between two paradigmatic quantum disordered states with distinct entanglement structures: the Kitaev quantum spin liquid and the Affleck-Kennedy-Lieb-Tasaki (AKLT) valence bond solid. Combining classical, semi-classical, and exact diagonalization approaches, we map out the ground-state phase diagram and elucidate the role of quantum fluctuations across the entire parameter range. While classical and semi-classical frameworks predict noncoplanar orders competing with a collinear Néel state, we find these phases to be fragile: once full quantum fluctuations are included, they melt into a quantum-entangled state characterized by suppressed spin correlations and enhanced entanglement entropy. Our findings highlight how competition between qualitatively different quantum disordered phases provides a fertile playground for unconventional phases emerging from their interplay and quantum fluctuations.

arXiv:2512.06322Physical review. B./Physical review. BMar 16, 20261 citation

Emergent infinite-randomness fixed points from the extensive random bipartitions of the spin-1 Affleck-Kennedy-Lieb-Tasaki topological state

Min Lu, Wen-Jia Rao, Rajesh Narayanan +2 more

Quantum entanglement under an extensive bipartition can reveal the critical boundary theory of a topological phase in a parameter space. In this study we demonstrate that the infinite-randomness fixed point for spin- $\frac{1}{2}$ degrees of freedom can emerge from an extensive random bipartition of the spin-1 Affleck-Kennedy-Lieb-Tasaki chain. The nested entanglement entropy of the ground state of the reduced density matrix exhibits a logarithmic scaling with an effective central charge $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{c}=0.72\ifmmode\pm\else\textpm\fi{}0.02\ensuremath{\approx}ln2$. We further discuss, in the language of bulk quantum entanglement, how to understand all phase boundaries and the surrounding Griffiths phases for the antiferromagnetic Heisenberg spin-1 chain with quenched disorder and dimerization.Quantum entanglement under an extensive bipartition can reveal the critical boundary theory of a topological phase in a parameter space. In this study we demonstrate that the infinite-randomness fixed point for spin-$\frac{1}{2}$ degrees of freedom can emerge from an extensive random bipartition of the spin-1 Affleck-Kennedy-Lieb-Tasaki chain. The nested entanglement entropy of the ground state of the reduced density matrix exhibits a logarithmic scaling with an effective central charge $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{c}=0.72\ifmmode\pm\else\textpm\fi{}0.02\ensuremath{\approx}ln2$. We further discuss, in the language of bulk quantum entanglement, how to understand all phase boundaries and the surrounding Griffiths phases for the antiferromagnetic Heisenberg spin-1 chain with quenched disorder and dimerization.

arXiv:1502.02095Physical review. B./Physical review. BDec 23, 20161 citation

The Affleck–Kennedy–Lieb–Tasaki (AKLT) model

Ian K. Affleck

The Haldane conjecture (1983), which led to a Nobel prize for Duncan Haldane, was that half-integer spin chains are gapless while integer spin chains are gapped. Haldane made this observation by a mapping onto a non-linear $\sigma$ -model at large spin. Gapless behavior for half-integer spin was proven rigorously by the Affleck–Lieb–Schultz–Mattis (ALSM) theorem. Gapped behavior for integer spin was demonstrated by an exactly solvable model known as Affleck–Kennedy–Lieb–Tasaki (AKLT) model (1987, 1988). In this review article, I will review the ALSM theorem and present results on the AKLT model. An important aspect of this model is that it has decoupled spin- $1/2$ ’s at the two ends with open boundary conditions. This was shown, by Kennedy (1990), to extend to the regular antiferromagnetic model. The first experimental demonstration of this behavior was in a paper by Hagiwara, Katsumata, Affleck, Halperin, and Renard (1990). I will review this experiment.The Haldane conjecture (1983), which led to a Nobel prize for Duncan Haldane, was that half-integer spin chains are gapless while integer spin chains are gapped. Haldane made this observation by a mapping onto a non-linear $\sigma$-model at large spin. Gapless behavior for half-integer spin was proven rigorously by the Affleck–Lieb–Schultz–Mattis (ALSM) theorem. Gapped behavior for integer spin was demonstrated by an exactly solvable model known as Affleck–Kennedy–Lieb–Tasaki (AKLT) model (1987, 1988). In this review article, I will review the ALSM theorem and present results on the AKLT model. An important aspect of this model is that it has decoupled spin-$1/2$’s at the two ends with open boundary conditions. This was shown, by Kennedy (1990), to extend to the regular antiferromagnetic model. The first experimental demonstration of this behavior was in a paper by Hagiwara, Katsumata, Affleck, Halperin, and Renard (1990). I will review this experiment.

EMS Press eBooksJun 29, 20220 citations

\mathrm{SU}(n)

We study spin-2 deformed-AKLT models on the square lattice, specifically a two-parameter family of

O(2)

-symmetric ground-state wave functions as defined by Niggemann, Kl\"umper, and Zittartz, who found previously that the phase diagram consists of a N\'eel-ordered phase and a disordered phase which contains the AKLT point. Using tensor-network methods, we not only confirm the N\'eel phase but also find an XY phase with quasi-long-range order and a region adjacent to it, within the AKLT phase, with very large correlation length, and investigate the consequences of a perfectly factorizable point at the corner of that phase.

\frac{1}{2}

degrees of freedom can emerge from an extensive random bipartition of the spin-1 Affleck-Kennedy-Lieb-Tasaki chain. The nested entanglement entropy of the ground state of the reduced density matrix exhibits a logarithmic scaling with an effective central charge $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{c}=0.72\ifmmode\pm\else\textpm\fi{}0.02\ensuremath{\approx}ln2$. We further discuss, in the language of bulk quantum entanglement, how to understand all phase boundaries and the surrounding Griffiths phases for the antiferromagnetic Heisenberg spin-1 chain with quenched disorder and dimerization.

\sigma

-model at large spin. Gapless behavior for half-integer spin was proven rigorously by the Affleck–Lieb–Schultz–Mattis (ALSM) theorem. Gapped behavior for integer spin was demonstrated by an exactly solvable model known as Affleck–Kennedy–Lieb–Tasaki (AKLT) model (1987, 1988). In this review article, I will review the ALSM theorem and present results on the AKLT model. An important aspect of this model is that it has decoupled spin-

1/2

’s at the two ends with open boundary conditions. This was shown, by Kennedy (1990), to extend to the regular antiferromagnetic model. The first experimental demonstration of this behavior was in a paper by Hagiwara, Katsumata, Affleck, Halperin, and Renard (1990). I will review this experiment.