Magnetic and Quasiparticle Excitation Spectra of an Itinerant<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>J</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>−</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>Model for Iron-Pnictide Superconductors

Conceição, C. M. S. da; Neto, M. B. Silva; Marino, E. C.

doi:10.1103/physrevlett.106.117002

Cited by 10 publications

(17 citation statements)

References 21 publications

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“…1 /2 [14,15], and thus acquires an imaginary part beyond the border at α < 0.5 when γ 0 > 2, showing that the magnetic excitations of the collinear state move from q = (π, 0) and/or q = (0, π) towards the one of the Néel state at q = (π, π), as expected. The complete phase diagram obtained within the NLSM formalism, for the whole range 0 ≤ α ≤ 1 is given in Fig.…”

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“…1, labelled A and B, which are decoupled when J 1 = 0. For J 1 = 0, however, two couplings arise: the first one involves only gradient terms and produces different spin-wave velocities along the diagonals [15]; the second, and more important one, is a result of the coupled pressession of magnetic moments on the two Néel sub-structures and modifies importantly the dynamics of the problem, ultimately leading to the first order character of the phase transition at α = 0.6.…”

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Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J ₁ -J ₂ Heisenberg model

Cysne¹,

Neto²

2015

EPL

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We obtain the complete phase diagram of the antiferromagnetic J1-J2 model, 0 ≤ α = J2/J1 ≤ 1, within the framework of the O(N ) nonlinear sigma model. We find two magnetically ordered phases, one with Néel order, for α ≤ 0.4, and another with collinear order, for α ≥ 0.6, separated by a nonmagnetic region, for 0.4 ≤ α ≤ 0.6, where a gapped spin liquid is found. The transition at α = 0.4 is of the second order while the one at α = 0.6 is of the first order and the spin gaps cross at α = 0.5. Our results are exact at N → ∞ and agree with numerical results from different methods. 74.72.Dn, 63.20.Ry, 63.20.dk Quantum phase transitions (QPTs) occur when the ground state properties of a certain physical system undergo dramatic changes as one, or more, internal or external, parameters are varied [1]. Examples include, but are not restricted to, magnetic phase transitions between two distinct magnetic ground states or between a magnetic state and a nonmagnetic one, driven for example by an applied field, pressure, or the coupling to oder degrees of freedom. QPTs are usually labelled according to the behaviour of some order parameter (OP) close to the quantum critical point (QCP) [2], and are said to be of the second order (2nd order) when the OP vanishes continuously as the QCP is approached, or of the first order (1st order) when the OP has a finite value near the QCP and jumps discontinuously to zero above it. Furthermore, knowledge of the range of the interactions, symmetries of the Hamiltonian and dimension of the OP, allow us to classify QPTs into universality classes [2], and help us to wirte down a Landau-Ginzburg free energy (LGFE) to describe such phase transitions (PTs). Typically, LGFEs up to the 4th power of the OP are enough to describe a 2nd order PT, while LGFEs up to the 6th power of the OP are necessary to describe a 1st order PT.The O(N ) quantum nonlinear sigma model (NLSM) has long been acknowledged to be a very convenient framework to describe 2nd order magnetic PTs in spin systems, such as, for example, the antiferromagnetic (AF) Heisenberg Hamiltonian, in two dimensions, with nearest-neighbour interactions on a square lattice [3]. Here the QPT occurs between a Néel ordered magnetic ground state, where the OP is the sublattice magnetization, σ = 0, and a nonmagnetic state (σ = 0) with a finite spin gap, ∆ = 0, as the OP at zero temperature. Such transition is driven by quantum fluctuations set by some coupling constant, g, and is of the 2nd order, as both σ and ∆ vanish continuously at the QCP, g c . Despite being nonlinear, at the mean field level (N → ∞) the model is quadratic, exactly solvable, and produces the usual mean field values for the critical exponents of the Heisenberg universality class, σ ∝ (g c − g) β , for the ordered regime (g < g c ), with β = 1/2, and ∆ ∝ (g − g c ) ν , for the nonmagnetic phase (g > g c ), with ν = 1 [4].First order PTs in spin systems occur whenever two magnetic phases cannot be continuously connected to one another by some order parameter. This is what ha...

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Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J ₁ -J ₂ Heisenberg model

Cysne¹,

Neto²

2015

EPL

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“…In the latter case, the RIXS instrumental resolution defines the single-magnon line width because of the long magnon lifetime. The larger observed magnon line width in the parent Fe pnictide is, however, not unexpected because its spin excitations, despite being well defined, are essentially damped by the interaction with itinerant electrons due to its metallic nature 9,30,33 . Carrier doping into the SC state does not necessarily add further damping of spin excitations, consistent with our RIXS observation (Fig.…”

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confidence: 97%

Persistent high-energy spin excitations in iron-pnictide superconductors

et al. 2013

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Motivated by the premise that superconductivity in iron-based superconductors is unconventional and mediated by spin fluctuations, an intense research effort has been focused on characterizing the spin-excitation spectrum in the magnetically ordered parent phases of the Fe pnictides and chalcogenides. For these undoped materials, it is well established that the spin-excitation spectrum consists of sharp, highly dispersive magnons. The fate of these highenergy magnetic modes upon sizable doping with holes is hitherto unresolved. Here we demonstrate, using resonant inelastic X-ray scattering, that optimally hole-doped superconducting Ba 0.6 K 0.4 Fe 2 As 2 retains well-defined, dispersive high-energy modes of magnetic origin. These paramagnon modes are softer than, though as intense as, the magnons of undoped antiferromagnetic BaFe 2 As 2 . The persistence of spin excitations well into the superconducting phase suggests that the spin fluctuations in Fe-pnictide superconductors originate from a distinctly correlated spin state. This connects Fe pnictides to cuprates, for which, in spite of fundamental electronic structure differences, similar paramagnons are present.

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“…Our results derived are found compatible with the earlier two-sublattice calculations [12][13][14] on the model, because the magnetic reference states, in the two limits that we consider, retains their two-sublattice nature. We emphasize at this point that the competing interaction pair ensures the four sublattice nature to the problem and, as a consequence, the appearance of multiple magnon branches in the system whose signatures are witnessed experimentally, e.g., in neutron diffraction results [16][17][18] in various frustrated magnetic systems.…”

Section: Introductionmentioning

confidence: 84%

Magnon dispersion and single hole motion in 2D frustrated antiferromagnets with four-sublattice structures

Kar

2015

Journal of Magnetism and Magnetic Materials

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We study a two dimensional spin-1 2 J1 −J2 antiferromagnet in a square lattice using the linearized spin wave theory recognizing the 4-sublattice nature of the underlying magnetic lattice. Multiple magnon modes with optical and acoustic branches about the stable Neel ordered and double acoustic branches about the columnar reference states are obtained for small and large values of λ(= J2/J1) respectively. An additional uniaxial anisotropy, for large λ, can lead to distinct spin gaps in such systems, as also witnessed experimentally. The single hole spectral behavior in a 2D t − J1 − J2 model, for small frustration, is then calculated within the non-crossing approximation. Our results match fairly well with exact diagonalization results from a 4 × 4 cluster. Hole spectral features and their evolution with λ resulting in "water-fall"-like smooth spectral weight transfer are discussed. Hole energy bands are identified and the corresponding energy-shift and reduction in width with spin-frustration are indicated.

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Magnetic and Quasiparticle Excitation Spectra of an ItinerantJ1−J2Model for Iron-Pnictide Superconductors

Cited by 10 publications

References 21 publications

Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J ₁ -J ₂ Heisenberg model

Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J ₁ -J ₂ Heisenberg model

Persistent high-energy spin excitations in iron-pnictide superconductors

Magnon dispersion and single hole motion in 2D frustrated antiferromagnets with four-sublattice structures

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Magnetic and Quasiparticle Excitation Spectra of an ItinerantJ1−J2Model for Iron-Pnictide Superconductors

Cited by 10 publications

References 21 publications

Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J 1 -J 2 Heisenberg model

Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J 1 -J 2 Heisenberg model

Persistent high-energy spin excitations in iron-pnictide superconductors

Magnon dispersion and single hole motion in 2D frustrated antiferromagnets with four-sublattice structures

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Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J ₁ -J ₂ Heisenberg model

Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J ₁ -J ₂ Heisenberg model