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Chuck-Hou Yee added In_the_Hg_cuprates_the__.tex
over 7 years ago
Commit id: 7eae221618bf4183fbcfb7f6937b677143b07c7d
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In the Hg-cuprates, the HgO$_\delta$ layer harbors dopant atoms which tune the
chemical potential. The BaO layers immediately adjacent to the CuO$_2$ plane
spatially separate the superconducting electrons from the detrimental effects
of the disordered dopant layer. Additionally, the highly ionic nature of the
BaO layer means they do not capture dopant electrons intended for the CuO$_2$
plane. The preference of Hg to be dumbbell coordinated bonds the entire
structure together without introducing structural distortions. Finally, the
highly ionic O-Hg-O dumbbells minimize $c$-axis hopping to maintain
2-dimensionality.
Due to their spatial proximity, the adjacent BaO layers tune the hoppings and
interaction strengths of the in-plane Hamiltonian. Designing compounds with
novel adjacent layers provides a mechanism for controlling superconductivity
by, e.g., reducing the charge-transfer energy. We quickly realized the most
stringent constraint is structural stability, so we focused first on isolating
stable candidates, then subsequently investigating their electronic properties.
To maximize the likelihood that a proposed composition is stable, we note that
the layers adjacent to the CuO$_2$ plane form a rock salt structure. Using
materials databases, we selected all naturally occurring rock salt compounds
AX, composed of an cation A and an anion X. The phase space is large and the
rate limiting step is structural prediction, so we quickly pre-screen
candidates by discarding compositions with (1) large lattice mismatches
relative to the in-plane Cu-Cu distance, which we took to be 3.82~\AA, and (2)
anions less electronegative than Cu, as these anions would capture dopants
intended for the superconducting plane, producing additional Fermi surfaces.
With the hindsight of
Revisisted with a and b done very well.
Outcome : proposed compound with more confidence.
Jury is out.
Discuss the notion of confidence.
Accuracy of LDA. Metastable structures do exist. One cuprates are above the hull.
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