Electronic structure of HgBa2Can−1CunO2n+2 (n = 1, 2, 3) superconductor parent compounds from periodic hybrid density functional theory

Systematic electronic structure in the cuprate parent state from quantum many-body simulations

The quantitative description of correlated electron materials remains a modern computational challenge. We demonstrate a numerical strategy to simulate correlated materials at the fully ab initio level beyond the solution of effective low-energy models and apply it to gain a detailed microscopic understanding across a family of cuprate superconducting materials in their parent undoped states. We uncover microscopic trends in the electron correlations and reveal the link between the material composition and magnetic energy scales through a many-body picture of excitation processes involving the buffer layers. Our work illustrates a path toward a quantitative and reliable understanding of more complex states of correlated materials at the ab initio many-body level.

Electronic and vibrational properties of the highTcsuperconductor Bi2Sr2CaCu2O8: anab initiostudy

In this work,ab initiocalculations were performed in order to study the vibrational spectra of the Bi₂Sr₂CaCu₂O₈(Bi2212) compound. A structural modulation correction on some atomic positions, producing a distorted structure with lower symmetry, is used for the calculation. We argue that this correction allows to account for an average effect of the incommensurate superstructure, generating a more accurate representation of the real unit cell observed in this compound. A complete and conclusive vibrational assignment is performed, discussing the correspondences with previous experimental and theoretical reports. A brief analysis of the electronic density of states and band structure comparing the tetragonal and distorted unit cell is also included.

Competing stripe and magnetic phases in the cuprates from first principles

Realistic description of competing phases in complex quantum materials has proven extremely challenging. For example, much of the existing density-functional-theory-based first-principles framework fails in the cuprate superconductors. Various many-body approaches involve generic model Hamiltonians and do not account for the interplay between the spin, charge, and lattice degrees of freedom. Here, by deploying the recently constructed strongly constrained and appropriately normed (SCAN) density functional, we show how the landscape of competing stripe and magnetic phases can be addressed on a first-principles basis both in the parent insulator YBa2Cu3O6 and the near-optimally doped YBa2Cu3O7 as archetype cuprate compounds. In YBa2Cu3O7, we find many stripe phases that are nearly degenerate with the ground state and may give rise to the pseudogap state from which the high-temperature superconducting state emerges. We invoke no free parameters such as the Hubbard U, which has been the basis of much of the existing cuprate literature. Lattice degrees of freedom are found to be crucially important in stabilizing the various phases.