High-TC Superconductivity in Hydrogen Clathrates Mediated by Coulomb Interactions Between Hydrogen and Central-Atom Electrons
The uniquely characteristic macrostructures of binary hydrogen-clathrate compounds M H n formed at high pressure, a cage of hydrogens surrounding a central-atom host, is theoretically predicted in various studies to include structurally stable phonon-mediated superconductors. High superconductive tr...
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| Published in | Journal of superconductivity and novel magnetism Vol. 33; no. 10; pp. 2945 - 2961 |
|---|---|
| Main Authors | , |
| Format | Journal Article |
| Language | English |
| Published |
New York
Springer US
01.10.2020
|
| Subjects | |
| Online Access | Get full text |
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| Summary: | The uniquely characteristic macrostructures of binary hydrogen-clathrate compounds
M
H
n
formed at high pressure, a cage of hydrogens surrounding a central-atom host, is theoretically predicted in various studies to include structurally stable phonon-mediated superconductors. High superconductive transition temperatures
T
C
have thus far been measured for syntheses with
M
= La, Y, and Th. In compressed LaH
10
, independent studies report
T
C
of 250 K and over 260 K, a maximum in
T
C
with pressure
P
, and normal-state resistance scaling with temperature (suggesting unconventional pairing). According to reported band structure calculations of
Fm
3
¯
m
-phase LaH
10
, the La is anionic, with the chemical valence electrons appearing evenly split between La and H
10
. Thus, compressed LaH
10
contains the combination of structure, charge separation, and optimal balanced allocation of valence electrons for supporting unconventional high-
T
C
superconductivity mediated by Coulomb interactions between electronic charges associated with La and H
10
. A general expression for the optimal superconducting transition temperature for
M
H
n
clathrates is derived as
T
C0
=
k
B
−1
Λ[(n +
v
)/2
A
]
1/2
e
2
/ζ, where Λ is a universal constant, (n +
v
) is the chemical valence sum per formula unit, taking unity for H and
v
for atom
M
,
A
is the surface area of the H-polyhedron cage, and ζ is the mean distance between the
M
site and the centroids of the polyhedron faces. Applied to
Fm
3
¯
m
LaH
10
,
T
C0
values of 249.8(1.3) K and 260.7(2.0) K are found for the two experiments. Associated attributes of charge allocation, structure, effective Coulomb potential, and H-D isotope effect in
T
C
of
Fm
3
¯
m
LaH
10
and
Im
3
¯
m
H
3
S are discussed, along with a generalized prospective for Coulomb-mediated superconductivity in
M
H
n
. |
|---|---|
| ISSN: | 1557-1939 1557-1947 |
| DOI: | 10.1007/s10948-020-05557-4 |