Multiorbital analysis of the effects of uniaxial and hydrostatic pressure onTcin the single-layered cuprate superconductors

Abstract

The origin of uniaxial and hydrostatic pressure effects on T c in the single-layered cuprate superconductors is theoretically explored. A two-orbital model, derived from first principles and analyzed with the fluctuation exchange approximation gives axial-dependent pressure coefficients ∂T c /∂P a > 0, ∂T c /∂P c < 0, with a hydrostatic response ∂T c /∂P > 0 for both La214 and Hg1201 cuprates, in qualitative agreement with experiments. Physically, this is shown to come from a unified picture in which higher T c is achieved with an "orbital distillation," namely, the less the d x 2 −y 2 main band is hybridized with the d z 2 and 4s orbitals the higher the T c . Some implications for obtaining higher T c materials are discussed.

Strain derivatives ofTcin HgBa2CuO4+δ: The CuOWang1, Zhang2, Yan3 et al. 2014Phys. Rev. B

“…A recent theoretical model which explicitly includes the Cu d x 2 −y 2 , d z 2 and 4s orbitals qualitatively predicts correctly the larger T c value of Hg1201 [36] and the sign of dT c /dP l and dT c /dP [37]. The model attributes the low T c of LSCO to the compound's body-centered tetragonal structure, in the close proximity of apical oxygen atoms of neighboring CuO 2 layers causes an elevation of the d z 2 Wannier orbital [38].…”

Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters and the two-band theory for Tc

“…In this regard, a notable suggestion has recently been made26272829. According to this theory, the T c of the single-layer cuprate can be described with a two-orbital model that considers both the and Wannier orbitals, and the energy level offset between the two orbitals, ΔE, plays a key role in determining T c .…”

“…However, while the theoretical Δ E or the Fermi surface shape was obtained from the LDA and used as the “inputs” for the many-body FLEX calculation in Refs 26, 27, 28, 29, the experimentally determined Δ E and the Fermi surface shape should be regarded as the “outputs” or “results” after the consideration of the many-body correlation effects beyond LDA/GGA. In fact, while a RIXS study reports that T c is higher for larger Δ E 32, the actual experimental value of Δ E is larger than the theoretical evaluation, presumably due to this “input vs. output” problem.…”

Zero Resistivity above 150 K in HgBa2Ca2Cu3O8+δat High Pressure

“…The possible origins are (1) a change in the effective carrier number owing to the redistribution of holes between outer and inner CuO 2 planes 13) and (2) a change in the hybridization within CuO 2 planes and/or that between CuO 2 planes and apical oxygen atoms. 14) Quantitative discussion can be made once the P-dependence of the crystal structures, including the atomic positions, are determined. Comparatively high-P studies of Hg-1201 and Hg-1212 are also helpful to sort out whether the charge transfer between the outer and inner CuO 2 planes is responsible for the enhancement in T c .…”