Strong correlation between electronic bonding network and critical temperature in hydrogen-based superconductors

Abstract

By analyzing structural and electronic properties of more than a hundred predicted hydrogen-based superconductors, we determine that the capacity of creating an electronic bonding network between localized units is key to enhance the critical temperature in hydrogen-based superconductors. We define a magnitude named as the networking value, which correlates with the predicted critical temperature better than any other descriptor analyzed thus far. By classifying the studied compounds according to their bonding nature, we observe that such correlation is bonding-type independent, showing a broad scope and generality. Furthermore, combining the networking value with the hydrogen fraction in the system and the hydrogen contribution to the density of states at the Fermi level, we can predict the critical temperature of hydrogen-based compounds with an accuracy of about 60 K. Such correlation is useful to screen new superconducting compounds and offers a deeper understating of the chemical and physical properties of hydrogen-based superconductors, while setting clear paths for chemically engineering their critical temperatures.

Mapping Superconductivity in High-Pressure Hydrides: The $Superhydra$ Project

“…Several empirical classification schemes have been proposed for binary hydrides, based on structural or chemical properties, such as interatomic distances, guest atom charge or atomic radius, electronegativity, electronic charge localization, etc. 18,19,21,37 .…”

“…For example, it was early recognized that in order for a superhydride to exhibit high-T c superconductivity, the interatomic H-H distance d HH should lie in a sweet spot between 0.9 and 1.35 Å 21 , and the hydrogen sublattice should be negatively charged 38 . Other authors recognized that high-T c superhydrides can be divided in two classes (covalent and clathrate hydrides), depending on the existence of a covalent bond between the A-H or a weakened H-H bond, 10 while Belli et al divided the known superhydrides in six classes (molecular, covalent, weak H interaction, electride, isolated and ionic), using an inspection of interatomic distances and electronic localization function profiles 21 .…”

“…Our result, however, confirms that all high-T c hydride superconductors share similar features: a relatively soft H lattice, where H-H interactions are much weaker than in H 2 molecules, but still strong enough to ensure H-H bonds (BM q , d HH ). This type of bonding becomes possible when enough negative charge is pumped into the hydrogen orbitals from other atoms acting as reservoirs (ρ H ) 21,32 . Moreover, the resulting electronic structure should also ensure that electrons in H bonds are actively involved in the superconductivity pairing (HDOS).…”

“…High-pressure superhydrides represent an ideal benchmark for such data-driven approaches, since firstprinciples calculations can provide accurate estimates for T c and overcome the limitations of scarcity and inhomogeneity of data associated with other classes of superconductors. Indeed, a few works in literature have attempted to study the distribution of T c , in binary hydrides applying empirical classification schemes to data previously published in literature [19][20][21] , or randomly-generated structures 9,18 . Both approaches present obvious intrinsic drawbacks: while datasets based on literature are usually limited to near-ground-state structures, losing precious information on other possible chemical environments, randomly-generated sets tend to contain many unphysical or unrepresentative structures 22 .…”

Lower pressure phases and metastable states of superconducting photo-induced carbonaceous sulfur hydride

“…[8] C-S-H, like hydrogen sulfide, is a covalent superhydride, wherein hydrogen is believed to form extended bonding networks with the other elements present. [9][10][11] This is opposed to the other main class of metal superhydides, which present as cage-like clathrate structures. The original theoretical attempts to identify candidate structures for C-S-H suggested a stoichiometry of CSH 7 .…”