Journal ArticleDOI
Transition temperature of strong-coupled superconductors reanalyzed
Philip B. Allen,Robert C. Dynes +1 more
TLDR
In this article, a through analysis of the dependence of the superconducting transition temperature on material properties is made, based on a combination of analytic and numerical solutions of the Eliashberg equations, and a comparison with tunneling data.Abstract:
A through analysis is made of the dependence of the superconducting transition temperature ${T}_{c}$ on material properties ($\ensuremath{\lambda}$, ${\ensuremath{\mu}}^{*}$, phonon spectrum) as contained in Eliashberg theory. The most striking new feature of the analysis is in the asymptotic regime of very large $\ensuremath{\lambda}$ where ${T}_{c}$ is found to equal $0.15 {(\ensuremath{\lambda}〈{\ensuremath{\omega}}^{2}〉)}^{\frac{1}{2}}$ (assuming ${\ensuremath{\mu}}^{*}=0.1$). This result implies the surprising conclusion that within Eliashberg theory ${T}_{c}$ is not limited by the phonon frequencies, and also shows that McMillan's "$\ensuremath{\lambda}=2$ limit" is spurious. The McMillan equation (with a prefactor altered from $\frac{{\ensuremath{\Theta}}_{D}}{1.45}$ to $\frac{{\ensuremath{\omega}}_{log}}{1.2}$) is found to be highly accurate for all known materials with $\ensuremath{\lambda}l1.5$ but in error for large values of $\ensuremath{\lambda}$. Correction factors to McMillan's equation are found in terms of $\ensuremath{\lambda}$, ${\ensuremath{\mu}}^{*}$, and one additional parameter, $\frac{{(〈{\ensuremath{\omega}}^{2}〉)}^{\frac{1}{2}}}{{\ensuremath{\omega}}_{log}}$. The frequency ${\ensuremath{\omega}}_{log}$ is defined as $\mathrm{exp} 〈\mathrm{ln}\ensuremath{\omega}〉$ where the averages $〈\mathrm{ln}\ensuremath{\omega}〉$ and $〈{\ensuremath{\omega}}^{2}〉$ are defined using $(\frac{2}{\ensuremath{\lambda}\ensuremath{\omega}}){\ensuremath{\alpha}}^{2}F(\ensuremath{\omega})$ as a weight factor. These conclusions are based on a combination of analytic and numerical solutions of the Eliashberg equations, and are supported by a comparison with tunneling data. Especially strong support comes from a new experimental result for amorphous ${\mathrm{Pb}}_{0.45}$${\mathrm{Bi}}_{0.55}$ reported herein. This material has parameters $\ensuremath{\lambda}=2.59$ and $\frac{{T}_{c}}{{\ensuremath{\omega}}_{log}}=0.284$, in serious disagreement with McMillan's formula but in good agreement when the correction factors are included. The McMillan-Hopfield parameter $\ensuremath{\eta}$ [or $N(0) 〈{I}^{2}〉$] is extracted from tunneling measurements or from a combination of empirical values of $\ensuremath{\lambda}$ and neutron-scattering measurements of phonon dispersion. It is proposed that $\ensuremath{\eta}$ (which is now known not to be accurately constant) is the most significant single parameter in understanding the origin of high ${T}_{c}$ and the limitation of ${T}_{c}$ by colvalent instabilities.read more
Citations
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Journal ArticleDOI
Electronic structure of the high-temperature oxide superconductors
TL;DR: In this paper, a review of the results of the density-functional type of electronic structure calculations is presented, and their results are compared with the relevant experimental data, showing that the important electronic states are dominated by the copper and oxygen orbitals, with strong hybridization between them.
Journal ArticleDOI
Electron-phonon interactions from first principles
TL;DR: The electron-phonon interaction in solids is important for many interesting properties of solids, among them the critical temperature of phonon-mediated superconductors, the effective electron mass in metals and semiconductors, and the carrier dynamics in semiconductor devices as discussed by the authors.
Journal ArticleDOI
Synthesis of clathrate cerium superhydride CeH9 at 80-100 GPa with atomic hydrogen sublattice.
Nilesh P. Salke,M. Mahdi Davari Esfahani,Youjun Zhang,Ivan A. Kruglov,Jianshi Zhou,Yaguo Wang,Eran Greenberg,Vitali B. Prakapenka,Jin Liu,Artem R. Oganov,Artem R. Oganov,Artem R. Oganov,Jung-Fu Lin +12 more
TL;DR: It is shown that CeH9 can be synthesized at 80-100 GPa with laser heating, and is characterized by a clathrate structure with a dense 3-dimensional atomic hydrogen sublattice, which shed a significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range.
Journal ArticleDOI
Superconductivity at 250 K in lanthanum hydride under high pressures
A. P. Drozdov,P. P. Kong,Vasily S. Minkov,S. P. Besedin,Mikhail A. Kuzovnikov,Shirin Mozaffari,Luis Balicas,Fedor Balakirev,David Graf,Vitali B. Prakapenka,Eran Greenberg,D. A. Knyazev,M. Tkacz,Mikhail Eremets +13 more
TL;DR: In this article, the authors reported superconductivity with a critical temperature of around 250 kelvin within the [Formula: see text] structure of LaH10 at a pressure of about 170 gigapascals.
Journal ArticleDOI
EPW: Electron-phonon coupling, transport and superconducting properties using maximally localized Wannier functions
TL;DR: The EPW (E lectron-P honon coupling using Wannier functions) as discussed by the authors software is a Fortran-90 code that uses density-functional perturbation theory and maximally localized WANier functions for computing electron-phonon couplings and related properties in solids accurately and efficiently.
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