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Register a new userInward dispersion of the spin excitation spectrum of stripe-ordered La2NiO4+d
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Polarized- and unpolarized-neutron scattering measurements of the spin excitation spectrum in the stripe-ordered phase of La2NiO4+d (d = 0.11) are presented. At low energies, the magnetic spectral weight is found to shift anomalously towards the two-dimensional antiferromagnetic wave vector, similar to the low-energy dispersions observed in cuprate superconductors. While spin-wave spectra in stripe phases can exhibit an apparent inward dispersion, we find that the peak shifts measured here cannot be accounted for by this effect. Possible extensions of the model are discussed.
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We report a detailed study of the temperature and magnetic-field dependence of the spin susceptibility for a single crystal of La(1.875)Ba(0.125)CuO(4). From a quantitative analysis, we find that the temperature-dependent anisotropy of the susceptibility, observed in both the paramagnetic and stripe-ordered phases, directly indicates that localized Cu moments dominate the magnetic response. A field-induced spin-flop transition provides further corroboration for the role of local moments. Contrary to previous analyses of data from polycrystalline samples, we find that a commonly-assumed isotropic and temperature-independent contribution from free carriers, if present, must be quite small. Our conclusion is strengthened by extending the quantitative analysis to include crystals of La(2-x)Ba(x)CuO(4) with x=0.095 and 0.155. On the basis of our results, we present a revised interpretation of the temperature and doping dependence of the spin susceptibility in La(2-x)(Sr,Ba)(x)CuO(4).
In the present work the multiband p-d model for $CuO_2$-layer is treated. It was shown that for the realistic set of parameters besides Zhang-Rice two-particle singlet there is non-negligible contribution of two-particle triplet state to the top of the valence band. Also shown, that to gain quantitative agreement with experimental data the minimal approximation should include the spin fluctuations beyond the Hubbard-I scheme. Quasiparticle spectrum, obtained in this approximation, is in fairly good agreement with ARPES data on Bi2212 High-$T_c$ compound.
In the stripe-ordered state of a strongly-correlated two-dimensional electronic system, under a set of special circumstances, the superconducting condensate, like the magnetic order, can occur at a non-zero wave-vector corresponding to a spatial period double that of the charge order. In this case, the Josephson coupling between near neighbor planes, especially in a crystal with the special structure of La_{2-x}Ba_xCuO_4, vanishes identically. We propose that this is the underlying cause of the dynamical decoupling of the layers recently observed in transport measurements at x=1/8.
We investigate the spin dynamics in the superconducting phase of UTe$_{2}$ by triple-axis inelastic neutron scattering on a single crystal sample. At the wave-vector $bf{k_1}$=(0, 0.57, 0), where the normal state antiferromagnetic correlations are peaked, a modification of the excitation spectrum is evidenced, on crossing the superconducting transition, with a reduction of the relaxation rate together with the development of an inelastic peak at $Omega$ $approx$ 1 meV. The low dimensional nature and the the $a$-axis polarization of the fluctuations, that characterise the normal state, are essentially maintained below $T_{sc}$. The high ratio $Omega/k_{B}T_{sc}$ $approx$ 7.2 contrasts with the most common behaviour in heavy fermion superconductors.
Magnetic interactions are widely believed to play a crucial role in the microscopic mechanism leading to high critical temperature superconductivity. It is therefore important to study the signatures of pairing in the magnetic excitation spectrum of simple models known to show unconventional superconducting tendencies. Using the Density Matrix Renormalization Group technique, we calculate the dynamical spin structure factor $S({bf k},omega)$ of a generalized $t-U-J$ Hubbard model away from half-filling in a two-leg ladder geometry. The addition of $J$ enhances pairing tendencies. We analyze quantitatively the signatures of pairing in the magnetic excitation spectra. We found that the superconducting pair-correlation strength, that can be estimated independently from ground state properties, is closely correlated with the integrated low-energy magnetic spectral weight in the vicinity of $(pi,pi)$. In this wave-vector region, robust spin incommensurate features develop with increasing doping. The branch of the spectrum with rung direction wave-vector $k_{rung}=0$ does not change substantially with doping where pairing dominates, and thus plays a minor role. We discuss the implications of our results for neutron scattering experiments, where the spin excitation dynamics of hole-doped quasi-one dimensional magnetic materials can be measured, and also address implications for recent resonant inelastic X-ray scattering experiments.
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