Quantum Phase Diagram of One-Dimensional Spin and Hubbard Models with Transitions to Bond Order Wave Phases

Kumar, Manoranjan; Ramasesha, S.; Soos, Z. G.

doi:10.5562/cca2324

Cited by 6 publications

(9 citation statements)

References 25 publications

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“…The BOW phase extends to arbitrarily large g according to Bursill et al 10 and the field theories of White and Affleck 11 and Itoi and Qin 13 . We find instead that the BOW phase terminates at 1/g** ~ 0.40 at the start of a gapless decoupled phase 21,22 with nondegenerate GS. We return in the Discussion to reasons for reexamining the quantum phase diagram at large g.…”

Section: Introductionmentioning

confidence: 65%

“…We have previously discussed 29,30 analytical results for spin chains with the J 2 term in Eq. 1 and long-range exchange that is not frustrating instead of the J 1 term.…”

Section: Discussionmentioning

confidence: 99%

“…We have previously discussed [29,30] analytical results for spin chains with the J 2 term in equation ( 1) and long-range exchange that is not frustrating instead of the J 1 term. Exact results are straightforward in models that conserve sublattice spin, and such models rigorously support a gapless decoupled QLRO(π/2) phase.…”

Section: Discussionmentioning

confidence: 99%

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Level crossing, spin structure factor and quantum phases of the frustrated spin-1/2 chain with first and second neighbor exchange

Kumar¹,

Parvej²,

Soos³

2015

J. Phys.: Condens. Matter

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Section: Introductionmentioning

confidence: 65%

“…We have previously discussed 29,30 analytical results for spin chains with the J 2 term in Eq. 1 and long-range exchange that is not frustrating instead of the J 1 term.…”

Section: Discussionmentioning

confidence: 99%

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Level crossing, spin structure factor and quantum phases of the frustrated spin-1/2 chain with first and second neighbor exchange

Kumar¹,

Parvej²,

Soos³

2015

J. Phys.: Condens. Matter

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“…The critical point Γ c is associated with the charge degrees of freedom of the MHM and has major consequences for NIT. The MHM also has a magnetic critical point Γ m due to spin degrees of freedom [35], a feature that was not recognized previously. The infinite chain is diamagnetic with a finite energy gap between the singlet ground state and the lowest triplet state for Γ > Γ m = −0.91.…”

Section: The Modified Hubbard Modelmentioning

confidence: 73%

Modeling the Neutral-Ionic Transition with Correlated Electrons Coupled to Soft Lattices and Molecules

2017

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Neutral-ionic transitions (NITs) occur in organic charge-transfer (CT) crystals of planar π-electron donors (D) and acceptors (A) that form mixed stacks . . . D +ρ A −ρ D +ρ A −ρ D +ρ A −ρ . . . with variable ionicity 0 < ρ < 1 and electron transfer t along the stack. The microscopic NIT model presented here combines a modified Hubbard model for strongly correlated electrons delocalized along the stack with Coulomb intermolecular interactions treated in mean field. It also accounts for linear coupling of electrons to a harmonic molecular vibration and to the Peierls phonon. This simple framework captures the observed complexity of NITs with continuous and discontinuous ρ on cooling or under pressure, together with the stack's instability to dimerization. The interplay of charge, molecular and lattice degrees of freedom at NIT amplifies the nonlinearity of responses, accounts for the dielectric anomaly, and generates strongly anharmonic potential energy surfaces (PES). Dynamics on the ground state PES address vibrational spectra using time correlation functions. When extended to the excited state PES, the NIT model describes the early (<1 ps) dynamics of transient NIT induced by optical CT excitation with a fs pulse. Although phenomenological, the model parameters are broadly consistent with density functional calculations.Keywords: neutral-ionic phase transition; charge transfer crystals; multistability; correlated electron models; structural instabilities; coupling to molecular and lattice vibrations; anharmonic vibrational spectra; polarization and polarizability; photoinduced phase transitions ForewordThe physics of strongly-correlated electron systems is characterized by a complex phenomenology that includes multiple competing phases, divergent responses, and anomalous metallic states [1]. In these materials the interplay between correlated electrons and phonons further enhances the complexity both in terms of the appearance of new phases and of amplification of materials responses. Mixed-stack charge-transfer (ms-CT) crystals offer an interesting opportunity to study strongly correlated electrons coupled to molecular vibrations and lattice modes. In these crystals, planar π-conjugated molecules with strong electron donor (D) and acceptor (A) character alternatively form face-to-face stacks. Electrons are delocalized along the stack, leading to fractional charge: . . .. . The most impressive demonstration of strong correlations in these systems is offered by the so-called neutral-ionic phase transition (NIT) [2], a transition from a valence insulator (ρ < 0.5) to a Mott insulator (ρ > 0.5), that can be induced by temperature [3], pressure [4], or even light [5][6][7][8][9]. Both continuous and discontinuous NITs are known, and a precise control of

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“…When acting together they therefore act to frustrate one another. A prototypical frustrated spin-lattice system is the spin- 1 2 J 1 -J 2 model on a one-dimensional (1D) chain [15,16] or a two-dimensional square lattice [17][18][19], in which the two competing terms in the Hamiltonian are isotropic Heisenberg spin-spin interactions between nearest-neighbor and next-nearest-neighbor pairs, with strength parameters J 1 ≡ λ 1 and J 2 ≡ λ 2 , respectively.…”

Section: Introductionmentioning

confidence: 99%

Generalized Phase-Space Techniques to Explore Quantum Phase Transitions in Critical Quantum Spin Systems

M.¹,

Rundle²,

Samson³

et al. 2022

Preprint

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We apply the generalized Wigner function formalism to detect and characterize a range of quantum phase transitions in several cyclic, finite-length, spin-1 2 one-dimensional spin-chain models, viz., the Ising and anisotropic XY models in a transverse field, and the XXZ anisotropic Heisenberg model. We make use of the finite system size to provide an exhaustive exploration of each system's singlesite, bipartite and multi-partite correlation functions. In turn, we are able to demonstrate the utility of phase-space techniques in witnessing and characterizing first-, second-and infinite-order quantum phase transitions, while also enabling an in-depth analysis of the correlations present within critical systems. We also highlight the method's ability to capture other features of spin systems such as ground-state factorization and critical system scaling. Finally, we demonstrate the generalized Wigner function's utility for state verification by determining the state of each system and their constituent sub-systems at points of interest across the quantum phase transitions, enabling interesting features of critical systems to be intuitively analyzed.

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Quantum Phase Diagram of One-Dimensional Spin and Hubbard Models with Transitions to Bond Order Wave Phases

Cited by 6 publications

References 25 publications

Level crossing, spin structure factor and quantum phases of the frustrated spin-1/2 chain with first and second neighbor exchange

Level crossing, spin structure factor and quantum phases of the frustrated spin-1/2 chain with first and second neighbor exchange

Modeling the Neutral-Ionic Transition with Correlated Electrons Coupled to Soft Lattices and Molecules

Generalized Phase-Space Techniques to Explore Quantum Phase Transitions in Critical Quantum Spin Systems

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