Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1708.02781

A gapped $Z_{2}$ spin liquid phase with a $U(1)$ mean field ansatz: a Bosonic resonating valence-bond description

Tao Li

Published Aug 9, 2017• 0 citations
arXivHTMLPDF

Abstract

Gapped $Z_{2}$ spin liquid as the simplest spin liquid has been proved to be the most difficult to realize in realistic models. Here we show that the frustration from a third-neighbor exchange $J_{3}$ on the spin-$\frac{1}{2}$ $J_{1}-J_{2}$ model on the square lattice may serve to stabilize such a long-sought state. We argue that a Bosonic RVB description is more appropriate than a Fermonic RVB description for such a gapped spin liquid phase. We show that while the mean field ansatz of the proposed state has a $U(1)$ gauge symmetry, the gauge fluctuation spectrum on it is actually gapped and the state should be understood rather as a $Z_{2}$ spin liquid state with topological order. The state is thus locally stable with respect to gauge fluctuation and can emerge continuously from a collinear Neel ordered phase.

DOI
10.48550/arxiv.1708.02781

Related papers

Gapped spin-liquid phase in the J1−J2 Heisenberg model by a bosonic resonating valence-bond ansatz

Tao Li, Federico Becca, Wen-Jun Hu +1 more

We study the ground-state phase diagram of the spin-$1/2$${J}_{1}\ensuremath{-}{J}_{2}$ Heisenberg model on the square lattice with an accurate bosonic resonating-valence-bond (RVB) wave function. In contrast to the RVB ansatz based on Schwinger fermions, the representation based on Schwinger bosons, supplemented by a variational Monte Carlo technique enforcing the exact projection onto the physical subspace, is able to describe a fully gapped spin liquid in the strongly frustrated regime. In particular, a fully symmetric ${Z}_{2}$ spin liquid is stable between two antiferromagnetic phases; a continuous transition at ${J}_{2}=0.4{J}_{1}$, when the Marshall sign rule begins to be essentially violated, and a first-order transition around ${J}_{2}=0.6{J}_{1}$ are present. Most importantly, the triplet gap is found to have a nonmonotonic behavior, reaching a maximum around ${J}_{2}=0.51{J}_{1}$, when the lowest spinon excitation moves from the $\ensuremath{\Gamma}$ to the $M$ point, i.e., $k=(\ensuremath{\pi},0)$.

arXiv:1205.3838•Physical Review B•Aug 7, 2012•62 citations

Z$_{2}$ spin liquid phase on the kagome lattice: a new saddle point

Tao Li

We have performed large scale variational search for the best RVB ansatz for the spin-$\frac{1}{2}$ kagome antiferromagnet with both nearest-neighboring(NN) and next-nearest-neighboring(NNN) exchanges assuming only translational symmetry. We find the best RVB state is always fully symmetric and has an mean field ansatz that is gauge equivalent to a previous proposed Z$_{2}$ spin liquid ansatz. The Z$_{2}$ state is found to be slightly more stable than the extensively studied U(1) gapless Dirac spin liquid state in both the $J_{2}\neq0$ and the $J_{2}=0$ case and to possess a small spinon gap for $J_{2}<0.2$. The breaking of the U(1) gauge symmetry in the Z$_{2}$ state is found to increase with $J_{2}$ and to be quite substantial around $J_{2}=0.15$. However, we find the Z$_{2}$ state is always very close to the gapless U(1) Dirac spin liquid state, although they have very different RVB parameters. We argue the kagome antiferromagnet should be better understood as a near critical system, rather than a system deep inside a gapped spin liquid phase with well established Z$_{2}$ topological order.

arXiv:1601.02165•Jan 9, 2016•5 citations

Continuous phase transition from Néel state to Z 2 spin-liquid state on a square lattice

Yang Qi, Zheng‐Cheng Gu

Recent numerical studies of the ${J}_{1}$-${J}_{2}$ model on a square lattice suggest a possible continuous phase transition between the N\'eel state and a gapped spin-liquid state with ${Z}_{2}$ topological order. We show that such a phase transition can be realized through two steps: First bring the N\'eel state to the U(1) deconfined quantum critical point, which has been studied in the context of N\'eel--valence bond solid (VBS) state phase transition. Then condense the spinon pair--skyrmion/antiskyrmion bound state, which carries both gauge charge and flux of the U(1) gauge field emerging at the deconfined quantum critical point. We also propose a Schwinger boson projective wave function to realize such a ${Z}_{2}$ spin liquid state and find that it has a relatively low variational energy ($\ensuremath{-}0.4893{J}_{1}$/site) for the ${J}_{1}$-${J}_{2}$ model at ${J}_{2}=0.5{J}_{1}$. The spin liquid state we obtain breaks the fourfold rotational symmetry of the square lattice and therefore is a nematic spin liquid state. This direct continuous phase transition from the N\'eel state to a spin liquid state may be realized in the ${J}_{1}$-${J}_{2}$ model, or the anisotropic ${J}_{1x}$-${J}_{1y}$-${J}_{2}$ model.

arXiv:1308.2759•Physical Review B•Jun 19, 2014•20 citations

Symmetric Z2 spin liquids and their neighboring phases on triangular lattice

Yuan-Ming Lu

Motivated by recent numerical discovery of a gapped spin liquid phase in spin-$1/2$ triangular-lattice ${J}_{1}\ensuremath{-}{J}_{2}$ Heisenberg model, we classify symmetric ${Z}_{2}$ spin liquids on triangular lattice in the Abrikosov-fermion representation. We find 20 phases with distinct spinon symmetry quantum numbers, eight of which have their counterparts in the Schwinger-boson representation. Among them we identify two promising candidates (#1 and #20), which can realize a gapped ${Z}_{2}$ spin liquid with up to next nearest neighbor mean-field amplitudes. We analyze their neighboring magnetic orders and valence bond solid patterns, and find one state (#20) that is connected to 120-degree Neel order by a continuous quantum phase transition. We also identify gapped nematic ${Z}_{2}$ spin liquids in the neighborhood of the symmetric states and find three promising candidates (#1, #6, and #20).

arXiv:1505.06495•Physical review. B./Physical review. B•Apr 11, 2016•58 citations

Deconfined criticality and a gapless Z 2 spin liquid in the square-lattice antiferromagnet

Henry Shackleton, Alex Thomson, Subir Sachdev A

The theory for the vanishing of N\'eel order in the spin $S=1/2$ square lattice antiferromagnet has been the focus of attention for many decades. A consensus appears to have emerged in recent numerical studies on the antiferromagnet with first and second neighbor exchange interactions (the ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model): A gapless spin liquid is present for a narrow window of parameters between the vanishing of the N\'eel order and the onset of a gapped valence bond solid state. We propose a deconfined critical SU(2) gauge theory for a transition into a stable ${\mathbb{Z}}_{2}$ spin liquid with massless Dirac spinon excitations; on the other side of the critical point, the SU(2) spin liquid (the `$\ensuremath{\pi}$-flux' phase) is presumed to be unstable to confinement to the N\'eel phase. We identify a dangerously irrelevant coupling in the critical SU(2) gauge theory, which contributes a logarithm-squared renormalization. This critical theory is also not Lorentz invariant and weakly breaks the SO(5) symmetry which rotates between the N\'eel and valence bond solid order parameters. We also propose a distinct deconfined critical U(1) gauge theory for a transition into the same gapless ${\mathbb{Z}}_{2}$ spin liquid; on the other side of the critical point, the U(1) spin liquid (the `staggered flux' phase) is presumed to be unstable to confinement to the valence bond solid. This critical theory has no dangerously irrelevant coupling, dynamic critical exponent $z\ensuremath{\ne}1$, and no SO(5) symmetry. All of these phases and critical points are unified in a SU(2) gauge theory with Higgs fields and fermionic spinons which can naturally realize the observed sequence of phases with increasing ${J}_{2}/{J}_{1}$: N\'eel, gapless ${\mathbb{Z}}_{2}$ spin liquid, and valence bond solid.

arXiv:2104.09537•Physical review. B./Physical review. B•Jul 6, 2021•27 citations

Topological Z2 resonating-valence-bond spin liquid on the square lattice

Ji-Yao Chen, Didier Poilblanc

A one-parameter family of long-range resonating-valence-bond (RVB) state on the square lattice was previously proposed to describe a critical spin liquid (SL) phase of the spin-1/2 frustrated Heisenberg model. We provide evidence that this RVB state in fact also realizes a topological (long-range entangled) ${\mathbb{Z}}_{2}$ SL, limited by two transitions to critical SL phases. The topological phase is naturally connected to the ${\mathbb{Z}}_{2}$ gauge symmetry of the local tensor. This Rapid Communication shows that, on one hand, spin-1/2 topological SL with ${C}_{4v}$ point-group symmetry and $SU(2)$ spin rotation symmetry exists on the square lattice and, on the other hand, criticality and nonbipartiteness are compatible. We also point out that strong similarities between our phase diagram and the ones of classical interacting dimer models suggest both can be described by similar Kosterlitz-Thouless transitions. This scenario is further supported by the analysis of the one-dimensional boundary state. Forms of parent Hamiltonians hosting the ${\mathbb{Z}}_{2}$ SL are suggested.

arXiv:1709.10019•Physical review. B./Physical review. B•Apr 11, 2018•26 citations
A gapped Z2Z_{2}Z2​ spin liquid phase with a U(1)U(1)U(1) mean field ansatz: a Bosonic resonating valence-bond description
Gapped Z2Z_{2}Z2​ spin liquid as the simplest spin liquid has been proved to be the most difficult to realize in realistic models. Here we show that the frustration from a third-neighbor exchange J3J_{3}J3​ on the spin-12\frac{1}{2}21​ J1−J2J_{1}-J_{2}J1​−J2​ model on the square lattice may serve to stabilize such a long-sought state. We argue that a Bosonic RVB description is more appropriate than a Fermonic RVB description for such a gapped spin liquid phase. We show that while the mean field ansatz of the proposed state has a U(1)U(1)U(1) gauge symmetry, the gauge fluctuation spectrum on it is actually gapped and the state should be understood rather as a Z2Z_{2}Z2​ spin liquid state with topological order. The state is thus locally stable with respect to gauge fluctuation and can emerge continuously from a collinear Neel ordered phase.
We study the ground-state phase diagram of the spin-1/21/21/2${J}_{1}\ensuremath{-}{J}_{2}$ Heisenberg model on the square lattice with an accurate bosonic resonating-valence-bond (RVB) wave function. In contrast to the RVB ansatz based on Schwinger fermions, the representation based on Schwinger bosons, supplemented by a variational Monte Carlo technique enforcing the exact projection onto the physical subspace, is able to describe a fully gapped spin liquid in the strongly frustrated regime. In particular, a fully symmetric Z2{Z}_{2}Z2​ spin liquid is stable between two antiferromagnetic phases; a continuous transition at J2=0.4J1{J}_{2}=0.4{J}_{1}J2​=0.4J1​, when the Marshall sign rule begins to be essentially violated, and a first-order transition around J2=0.6J1{J}_{2}=0.6{J}_{1}J2​=0.6J1​ are present. Most importantly, the triplet gap is found to have a nonmonotonic behavior, reaching a maximum around J2=0.51J1{J}_{2}=0.51{J}_{1}J2​=0.51J1​, when the lowest spinon excitation moves from the $\ensuremath{\Gamma}$ to the MMM point, i.e., $k=(\ensuremath{\pi},0)$.
Z2_{2}2​ spin liquid phase on the kagome lattice: a new saddle point
We have performed large scale variational search for the best RVB ansatz for the spin-12\frac{1}{2}21​ kagome antiferromagnet with both nearest-neighboring(NN) and next-nearest-neighboring(NNN) exchanges assuming only translational symmetry. We find the best RVB state is always fully symmetric and has an mean field ansatz that is gauge equivalent to a previous proposed Z2_{2}2​ spin liquid ansatz. The Z2_{2}2​ state is found to be slightly more stable than the extensively studied U(1) gapless Dirac spin liquid state in both the J2≠0J_{2}\neq0J2​=0 and the J2=0J_{2}=0J2​=0 case and to possess a small spinon gap for J2<0.2J_{2}<0.2J2​<0.2. The breaking of the U(1) gauge symmetry in the Z2_{2}2​ state is found to increase with J2J_{2}J2​ and to be quite substantial around J2=0.15J_{2}=0.15J2​=0.15. However, we find the Z2_{2}2​ state is always very close to the gapless U(1) Dirac spin liquid state, although they have very different RVB parameters. We argue the kagome antiferromagnet should be better understood as a near critical system, rather than a system deep inside a gapped spin liquid phase with well established Z2_{2}2​ topological order.
Recent numerical studies of the J1{J}_{1}J1​-J2{J}_{2}J2​ model on a square lattice suggest a possible continuous phase transition between the N\'eel state and a gapped spin-liquid state with Z2{Z}_{2}Z2​ topological order. We show that such a phase transition can be realized through two steps: First bring the N\'eel state to the U(1) deconfined quantum critical point, which has been studied in the context of N\'eel--valence bond solid (VBS) state phase transition. Then condense the spinon pair--skyrmion/antiskyrmion bound state, which carries both gauge charge and flux of the U(1) gauge field emerging at the deconfined quantum critical point. We also propose a Schwinger boson projective wave function to realize such a Z2{Z}_{2}Z2​ spin liquid state and find that it has a relatively low variational energy ($\ensuremath{-}0.4893{J}_{1}$/site) for the J1{J}_{1}J1​-J2{J}_{2}J2​ model at J2=0.5J1{J}_{2}=0.5{J}_{1}J2​=0.5J1​. The spin liquid state we obtain breaks the fourfold rotational symmetry of the square lattice and therefore is a nematic spin liquid state. This direct continuous phase transition from the N\'eel state to a spin liquid state may be realized in the J1{J}_{1}J1​-J2{J}_{2}J2​ model, or the anisotropic J1x{J}_{1x}J1x​-J1y{J}_{1y}J1y​-J2{J}_{2}J2​ model.
Motivated by recent numerical discovery of a gapped spin liquid phase in spin-1/21/21/2 triangular-lattice ${J}_{1}\ensuremath{-}{J}_{2}$ Heisenberg model, we classify symmetric Z2{Z}_{2}Z2​ spin liquids on triangular lattice in the Abrikosov-fermion representation. We find 20 phases with distinct spinon symmetry quantum numbers, eight of which have their counterparts in the Schwinger-boson representation. Among them we identify two promising candidates (#1 and #20), which can realize a gapped Z2{Z}_{2}Z2​ spin liquid with up to next nearest neighbor mean-field amplitudes. We analyze their neighboring magnetic orders and valence bond solid patterns, and find one state (#20) that is connected to 120-degree Neel order by a continuous quantum phase transition. We also identify gapped nematic Z2{Z}_{2}Z2​ spin liquids in the neighborhood of the symmetric states and find three promising candidates (#1, #6, and #20).
The theory for the vanishing of N\'eel order in the spin S=1/2S=1/2S=1/2 square lattice antiferromagnet has been the focus of attention for many decades. A consensus appears to have emerged in recent numerical studies on the antiferromagnet with first and second neighbor exchange interactions (the ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model): A gapless spin liquid is present for a narrow window of parameters between the vanishing of the N\'eel order and the onset of a gapped valence bond solid state. We propose a deconfined critical SU(2) gauge theory for a transition into a stable Z2{\mathbb{Z}}_{2}Z2​ spin liquid with massless Dirac spinon excitations; on the other side of the critical point, the SU(2) spin liquid (the `$\ensuremath{\pi}$-flux' phase) is presumed to be unstable to confinement to the N\'eel phase. We identify a dangerously irrelevant coupling in the critical SU(2) gauge theory, which contributes a logarithm-squared renormalization. This critical theory is also not Lorentz invariant and weakly breaks the SO(5) symmetry which rotates between the N\'eel and valence bond solid order parameters. We also propose a distinct deconfined critical U(1) gauge theory for a transition into the same gapless Z2{\mathbb{Z}}_{2}Z2​ spin liquid; on the other side of the critical point, the U(1) spin liquid (the `staggered flux' phase) is presumed to be unstable to confinement to the valence bond solid. This critical theory has no dangerously irrelevant coupling, dynamic critical exponent $z\ensuremath{\ne}1$, and no SO(5) symmetry. All of these phases and critical points are unified in a SU(2) gauge theory with Higgs fields and fermionic spinons which can naturally realize the observed sequence of phases with increasing J2/J1{J}_{2}/{J}_{1}J2​/J1​: N\'eel, gapless Z2{\mathbb{Z}}_{2}Z2​ spin liquid, and valence bond solid.
A one-parameter family of long-range resonating-valence-bond (RVB) state on the square lattice was previously proposed to describe a critical spin liquid (SL) phase of the spin-1/2 frustrated Heisenberg model. We provide evidence that this RVB state in fact also realizes a topological (long-range entangled) Z2{\mathbb{Z}}_{2}Z2​ SL, limited by two transitions to critical SL phases. The topological phase is naturally connected to the Z2{\mathbb{Z}}_{2}Z2​ gauge symmetry of the local tensor. This Rapid Communication shows that, on one hand, spin-1/2 topological SL with C4v{C}_{4v}C4v​ point-group symmetry and SU(2)SU(2)SU(2) spin rotation symmetry exists on the square lattice and, on the other hand, criticality and nonbipartiteness are compatible. We also point out that strong similarities between our phase diagram and the ones of classical interacting dimer models suggest both can be described by similar Kosterlitz-Thouless transitions. This scenario is further supported by the analysis of the one-dimensional boundary state. Forms of parent Hamiltonians hosting the Z2{\mathbb{Z}}_{2}Z2​ SL are suggested.