Spin-spectral-weight distribution and energy range of the parent compound La ₂ CuO ₄

Abstract

The spectral-weight distribution in recent neutron scattering experiments on the parent compound La2CuO4 (LCO), which are limited in energy range to about 450 meV, is studied in the framework of the Hubbard model on the square lattice. We find that the higher-energy weight extends to about 566 meV and is located at and near the momentum [π, π]. Our results confirm that the U/t value suitable to LCO is in the range U/t ∈ (6, 8). The continuum weight energy-integrated intensity vanishes or is extremely small at momentum [π, 0]. This behavior of the intensity is consistent with that of spin waves, which are damped at [π, 0]. PACS numbers: 78.70.Nx, 74.72.Cj, 71.10.Fd, 71.10.Hf It is natural to expect that a greater understanding of the physics of the high-T c superconductor undoped parent compounds, such as La 2 CuO 4 (LCO), will lead to a greater understanding of the corresponding superconductors. In particular, the less complicated undoped systems can provide valuable information on which model Hamiltonians quantitatively describe the cuprates. Improved determination of the model Hamiltonians is essential because of the many nearby competing phases in the doped systems, easily affected by small parameters, which can now be seen because of continued improvements in numerical simulations [1]. A decade ago the neutron scattering experiments on LCO of Coldea, et. al. [2] first showed sufficient details of the spin-wave spectrum to demonstrate that a simple nearest-neighbor Heisenberg model must be supplemented by a number of additional terms, including ring exchanges. These terms arise naturally out of a single band Hubbard model with finite U/t, and several detailed studies showed that the spin-wave data in the available energy window could be successfully described by the Hubbard model using a somewhat smaller value of U/t ∼ 6 − 8 than originally thought appropriate [2][3][4][5]. However, part of the spectral weight was deduced to be outside the energy window.Recently, improved neutron scattering experiments [6] with a much wider energy window of about 450 meV, have raised a number of questions. Surprisingly, these studies revealed that the high-energy spin waves are strongly damped near momentum [π, 0] and merge into a momentum-dependent continuum. These results led the authors of Ref.[6] to conclude that "the ground state of La 2 CuO 4 contains additional correlations not captured by the Néel-SWT [spin-wave theory] picture". This raises the important question of whether the more detailed results can still be described in terms of a simple Hubbard model. Here we address this question using a combination of a number of theoretical and numerical approaches, including, in addition to standard treatments, a new spinon approach for the spin excitations [5,7] and density matrix renormalization group (DMRG) calculations for Hubbard cylinders [8][9][10]. We show that the Hubbard model does describe the new neutron scattering results. In particular, at momentum [π, 0] the continuum weight energy-integrated intensity i...

Direct theoretical evidence for weaker correlations in electron-doped and Hg-based hole-doped cuprates

“…The calculated U/t for La 2 CuO 4 is ∼7 which compares reasonably well with the widely used values for the model Hamiltonian studies [25]. The U/t value for the RE 2 CuO 4 series is ∼3, which is significantly smaller (∼43% of the La 2 CuO 4 value).…”

“…2; the data in green color and the right vertical axis), where the nearest-neighbor hopping parameter, t , was calculated with the standard Wannier-function technique2324 (see Supplementary Information). The calculated U / t for La 2 CuO 4 is ~7 which compares reasonably well with the widely used values for the model Hamiltonian studies25. The U / t value for the RE 2 CuO 4 series is ~3, which is significantly smaller (~43% of the La 2 CuO 4 value).…”