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Chuck-Hou Yee edited cuprates1.tex
almost 8 years ago
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The cuprate superconductors are a classic example of correlate materials, where the sizable onsite Coulomb interaction on the copper 3$d$ orbitals is comparable with the kinetic energy of the electrons. Since the family of compounds exhibits the highest known superconducting transition temperatures at ambient pressure (superceded only by H$_3$S at extremely high pressures), they have been intensely studied since their discovery in the mid 1980s. Here, rather than pursuing low-energy model hamiltonians, we took a chemical approach and asked how could the chemistry of the materials be leveraged to tune superconductivity.
Specifically, we
ask asked what chemical parameters
are very
to cross across the
coop rights cuprates to give transition temperatures ranging from below 40K to over 130K. Based on a combination of first principles calculations and dynamical meaning field theory to directly model the superconducting state, we found that varying the charge transfer energy
to tunes superconductivity.
Specifically, LSCO has the largest charge transfer energy and a small Tc. Moving across the cuprate family we found that as the charge transfer energy was reduced, the transition temperature increased. Inspired by this finding, we sought to design a new family of cuprates with reduced charge transfer gaps in hopes of finding higher transition temperatures.
Qualitative Idea. Reducing Work by Zanaan, Sawatzsky and Allan showed that the relative alignment of the oxygen 2$p$ and copper 3$d$ orbital levels combined with the magnitude of the onsite repulsion $U$ controls the charge transfer
gap, increase Tc in cuprate like structures.
a) DMFT energy. Dynamical mean-field calculations corroborated this picture by showing how the spectral charge transfer energy varies with the underline parameters of the hamiltonian. Additionally, density functional theory showed that the distance of the apical oxygen from the CuO$_2$ plane there is a charge transfer energy. Since we wanted to
compute gap. reduce the charge transfer energy to produce higher Tc's, we replaced the apical oxygen with sulfur, reasoning that its more extended 3$p$ orbitals would screen and reduce the strength of the in plane correlations.
b) Local checks. In plane rotations. No global structural optimization.
...
More work shows that that slices give a different picture.
Outcome BirdOutcome : do any of these materials exist ?
Corrections to LDA/GGA energies for convex hull construction have been systematically investigated for transition metal oxides [PRB 73, 195107 (2006), PRB 84, 045115 (2011)]. The corrections arise from two sources: (a) the GGA overbinding of the anion (most commonly the $O_2$ molecule) and (b) correlations. The GGA overbinding differs based on the anion, and the corrections are tabulated in the Materials Project.