# Symmetry-Shaped
Singularities in High-Temperature
Superconductor H_{3}S

journal contribution

posted on 2024-06-25, 14:35 authored by Sebastian
R. Thomsen, Maarten G. GoestenThe superconducting critical temperature
of H

_{3}S ranks among the highest measured, at 203 K. This impressive value stems from a singularity in the electronic density-of-states, induced by a flat-band region that consists of saddle points. The peak sits right at the Fermi level, so that it gives rise to a giant electron–phonon coupling constant. In this work, we show how atomic orbital interactions and space group symmetry work in concert to shape the singularity. The body-centered cubic Brillouin Zone offers a unique 2D hypersurface in reciprocal space: fully connecting squares with two different high-symmetry points at the corners, Γ and H, and a third one in the center, N. Orbital mixing leads to the collapse of fully connected 1D saddle point lines around the square centers, due to a symmetry-enforced s-p energy inversion between Γ and H. The saddle-point states are invariably nonbonding, which explains the unconventionally weak response of the superconductor’s critical temperature to pressure. Although H_{3}S appears to be a unique case, the theory shows how it is possible to engineer flat bands and singularities in 3D lattices through symmetry considerations.## History

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unconventionally weak responsepeak sits rightp energy inversionorbital mixing leadsimpressive value stemsfully connecting squaresatomic orbital interactionsunique 2d hypersurfacesuperconducting critical temperaturetwo different highengineer flat bands3 temperature superconductor hcritical temperatureunique casesuperconductor ’third onetheory showssquare centersreciprocal spaceranks amonginvariably nonbondinghighest measuredgives risefermi levelelectronic densityband regionalthough h3d lattices203 k

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