Numerical study of incommensurate and decoupled phases of spin-1/2 chains with isotropic exchangeJ1,J2between first and second neighbors

Soos, Z. G.; Parvej, Aslam; Kumar, Manoranjan

doi:10.1088/0953-8984/28/17/175603

Cited by 37 publications

(42 citation statements)

References 49 publications

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“…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. The singlet-triplet gap is zero for Γ ≤ Γ m , and the infinite chain is paramagnetic with finite magnetic susceptibility at 0 K. Quantum phase transitions related to the opening of a singlet-triplet gap have been extensively treated theoretically in spin-1/2 chains with frustrated exchange interactions [36][37][38] and in half-filled extended Hubbard models [39][40][41]. The magnetic critical point has no role so far in NIT models, mainly due to structural instabilities that are discussed below.…”

Section: The Modified Hubbard Modelmentioning

confidence: 99%

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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Section: The Modified Hubbard Modelmentioning

confidence: 99%

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

2017

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“…The GS is a singlet, S G = 0, in the entire sector J 1 , J 2 > 0 that includes spin liquid phase and gapped dimer or incommensurate phases. 10 All ladders in this paper have identical legs with J 2 = 1 in Eq. 1 and different numbers of J 1 rungs.…”

Section: Introductionmentioning

confidence: 99%

Quantum phases of frustrated two-leg spin- 12 ladders with skewed rungs

et al. 2017

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The quantum phases of 2-leg spin-1/2 ladders with skewed rungs are obtained using exact diagonalization of systems with up to 26 spins and by density matrix renormalization group calculations to 500 spins. The ladders have isotropic antiferromagnetic (AF) exchange J2 > 0 between first neighbors in the legs, variable isotropic AF exchange J1 between some first neighbors in different legs, and an unpaired spin per odd-membered ring when J1 J2. Ladders with skewed rungs and variable J1 have frustrated AF interactions leading to multiple quantum phases: AF at small J1, either F or AF at large J1, as well as bond-order-wave phases or reentrant AF (singlet) phases at intermediate J1.

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“…For J 2 /|J 1 | < 0.25, the gs of an isolated zigzag ladder has ferromagnetically ordered spins and gapless excitations. In the intermediate parameter regime, 0.25 < J 2 /|J 1 | < 0.67, NC order arises in this system with a small finite spin gap [4][5][6]39]. The system behaves like two decoupled AFM chains exhibiting QLRO in spin-spin correlation and gapless excitations in J 2 /|J 1 | > 0.67 limit [6].…”

Section: Resultsmentioning

confidence: 95%

“…In the last couple of decades frustrated low dimensional quantum magnets have been intensively explored in search of various exotic phases like spin fluid with quasi-long-range order (QLRO) [1][2][3][4][5][6], spin dimer with short-range order (SRO) [2,3,[7][8][9], vector chiral [10,11], multipolar phases [10][11][12][13] etc. These phases arise in presence of some specific types of spin exchange interactions which may enhance the quantum fluctuations in low-dimensional frustrated systems like one dimensional (1D) spin chains realized in materials, LiCuVO 4 [14], Li 2 CuZrO 4 [15], Li 2 CuSbO 4 [16], (N 2 H 5 )CuCl 3 [17] etc., and quasi-1D spin ladders manifested in form of SrCu 2 O 3 [18], (VO) 2 P 2 O 7 [19,20] etc.…”

Section: Introductionmentioning

confidence: 99%

Quantum phase diagram of a frustrated spin- 12 system on a trellis ladder

Maiti

Kumar

2019

Phys. Rev. B

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We study an isotropic Heisenberg spin-1/2 model on a trellis ladder which is composed of two J1 − J2 zigzag ladders interacting through anti-ferromagnetic rung couplings J3. The J1 and J2 are ferromagnetic zigzag spin interaction between two legs and anti-ferromagnetic interaction along each leg of a zigzag ladder. A quantum phase diagram of this model is constructed using the density matrix renormalization group (DMRG) method and linearized spin wave analysis. In small J2 limit a short range stripe collinear phase is found in the presence of J3, whereas, in the large J2/J3 limit non-collinear quasi-long range phase is found. The system shows a short range non-collinear state in large J3 limit. The short range order phase is the dominant feature of this phase diagram. We also show that the results obtained by DMRG and linearized spin wave analysis show similar phase boundary between stripe collinear and non-collinear short range phases, and the collinear phase region shrinks with increasing J3. We apply this model to understand the magnetic properties of CaV2O5 and also fit the experimental data of susceptibility and magnetization. The variation of magnetic specific heat capacity as function of external magnetic field is also predicted. We note that J3 is a dominant interaction in this system, whereas J1 and J2 are approximately half of J3.

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Numerical study of incommensurate and decoupled phases of spin-1/2 chains with isotropic exchangeJ₁,J₂between first and second neighbors

Cited by 37 publications

References 49 publications

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

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

Quantum phases of frustrated two-leg spin- 12 ladders with skewed rungs

Quantum phase diagram of a frustrated spin- 12 system on a trellis ladder

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