Spin and charge fluctuations in theU−t−t′model

Abstract

As additional neutron scattering experiments are performed on a variety of high temperature superconducting compounds it appears that magnetic incommensuration is a phenomenon common to all of the samples studied. The newest experimental results indicate that incommensurate peaks exist at momentum q = π(1, 1 ± δ) and π(1 ± δ, 1) in La2−xSrxCuO4 (LSCO) and YBa2Cu3O 7−δ (YBCO). The dependence of δ with hole doping appears to be similar in both materials. In addition, new ARPES data for LSCO as a function of doping show that its Fermi surface is qualitatively similar to the one of YBCO, contrary to what was previously believed. Early theoretical attempts to explain LSCO and YBCO behavior usually relied on one-or three-band Hubbard models or the t-J model with electron hopping beyond nearest-neighbor and with different parameter values for each material. In this paper it is shown that using a one band Hubbard U-t-t ′ model with a unique set of parameters, U/t=6 and t ′ /t=-0.25, good agreement is obtained between computational calculations and neutron scattering and ARPES experiments for LSCO and YBCO. It is also shown that using a more negative t ′ /t will induce short-range magnetic incommensuration along the diagonal direction in the Brillouin zone, in qualitative disagreement with the experimental results. At the finite temperatures of the present Monte Carlo simulation it is also observed that in this model the tendency to incommensuration appears to be more related to the shape of the two-dimensional Fermi surface and the strength of the interaction, rather than to charge order.

Quantum Monte Carlo study of Spin, Charge, and Pairing correlations in thet−t′−UHubbard model

“…Hole doping away from half filling rapidly decreases this long-range order. 6,[15][16][17]19,24 A similar decrease is seen experimentally. A nonzero value of tЈ seems necessary to mimic at least some of the features in the static spin structure factor seen in neutron diffraction experiments.…”

“…A close examination of these figures reveals that the spin structure along the zone boundaries and the line ⌬ connecting (,0) and (0,0) is nearly identical for the two cases, that is, virtually independent of electron density. We also note that Buhler and Moreo's QMC work 24 indicates that the spin structure factor for Uϭ6.0, ͗n͘ϭ0.7 on the 8ϫ8 lattice exhibits incommensurate structure on the zone diagonal ⌺ when tЈϽϪ0. 15.…”

“…Neutron scattering studies on La x Sr 1Ϫx CuO 4 and now other cuprates showed peaks in the spin structure at the incommensurate wave vector positions Q ជ ϭ(1,1Ϯ⑀) and (1Ϯ⑀,1) on the Brillouin zone face. While a recent QMC study 24 of the t-tЈ-U models reaffirmed this, it also reported incommensurate peaks along the zone diagonal sometimes occur. Consistency with experiment thus requires material dependent, restricted values of tЈ/t.…”

Collective modes in the paramagnetic phase of the Hubbard model

“…Early QMC simulations of the Hubbard model have been mainly focused on the static spin and charge structure factors [60][61][62]. As previously discussed in Ref.…”

The t‐U‐V‐J model in cuprates: Strengths of the interactions

“…The two models predict phase instabilities which give rise to a divergence of the charge density and spin response functions, and therefore, they have been the focus of particular interest as models for high-temperature superconductivity. In particular, the commensurate and incommensurate peak structures associated with the neutron cross section have been studied within the Fermi-liquid-based scenario using the single-band Hubbard t -U model [1][2][3], or the t -J model [4][5][6][7][8][9]. Common to t -U and t -J models is the expression for the magnetic susceptibility in the random phase approximation (RPA) χ RP A (Q, ω) = χ (0) (Q, ω)/ 1 + ϕ(Q)χ (0) (Q, ω) , where χ (0) (Q, ω) is the bare magnetic susceptibility, ϕ(Q) = U in the case of the t -U model, and ϕ(Q) = −2J (cosQ x + cosQ y ) in the case of a nearest-neighbor AF interaction.…”