Non-linear self-consistent screening applied to metallic hydrogen

1979 ◽  
Vol 57 (8) ◽  
pp. 1185-1195 ◽  
Author(s):  
M. D. Whitmore ◽  
J. P. Carbotte ◽  
R. C. Shukla
Keyword(s):  
Harmonic Approximation ◽  
Spherical Approximation ◽  
Face Centered Cubic ◽  
Superconducting Transition ◽  
Metallic Hydrogen ◽  
Proton Proton ◽  
Effective Electron ◽  
Functional Derivatives ◽  
Self Consistent ◽  
Non Linear

Non-linear self-consistent screening of a proton by a high density electron gas has been used to find effective electron–proton potentials for metallic hydrogen for a number of densities and for both face-centered cubic and body-centered cubic structures. The resulting proton–proton potentials have been employed to calculate the phonons in the self-consistent harmonic approximation, following which the effective distributions α2F(ω) were evaluated in the plane wave, spherical approximation. From these, the superconducting transition temperatures Te and functional derivatives were found.Non-linear effects are seen to be important. For both structures, dynamical instabilities occur for rs ≥ 1.0, indicating densities higher than those predicted by linear theory are required. In addition, for the fcc case, Te is enhanced.Te is found to depend sensitively on the structure assumed; for the bcc case, it is very small.For fcc H. McMillan's equation overestimates Te by about 40%, even when λ = 0.5. Leavens' formula agrees with solutions of the Eliashberg gap equations to within about 10%.

scholarly journals Quantum effects in muon spin spectroscopy within the stochastic self-consistent harmonic approximation

2019 ◽  
Vol 3 (7) ◽  
Author(s):  
Ifeanyi John Onuorah ◽  
Pietro Bonfà ◽  
Roberto De Renzi ◽  
Lorenzo Monacelli ◽  
Francesco Mauri ◽  
...  
Keyword(s):  
Muon Spin ◽  
Harmonic Approximation ◽  
Quantum Effects ◽  
Self Consistent ◽  
Muon Spin Spectroscopy

CRUCIAL ROLE OF THE COULOMB INTERACTION IN HTSC MECHANISM

2005 ◽  
Vol 19 (01n03) ◽  
pp. 107-109 ◽  
Author(s):  
E. A. PASHITSKII ◽  
V. I. PENTEGOV
Keyword(s):  
Coulomb Interaction ◽  
Vertex Function ◽  
Cooper Pairing ◽  
Superconducting Transition ◽  
Coulomb Correlation ◽  
Critical Temperatures ◽  
Effective Electron ◽  
Electron Attraction ◽  
D Wave

We present results of numerical calculations emphasizing the central role of the Coulomb interaction in the mechanism of d-wave Cooper pairing in layered cuprate metal-oxides. We demonstrate that many-particle Coulomb correlation described by the Coulomb vertex function Γ substantially enhances the effective electron-electron attraction in the d-wave Cooper-pairing channel in these compounds. Such a "Coulomb" mechanism of anisotropic Cooper pairing may provide high superconducting transition critical temperatures (Tc⩾100 K ) for optimum-doped cuprates.

scholarly journals Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure

2017 ◽  
Vol 114 (27) ◽  
pp. 6990-6995 ◽  
Author(s):  
Hanyu Liu ◽  
Ivan I. Naumov ◽  
Roald Hoffmann ◽  
N. W. Ashcroft ◽  
Russell J. Hemley
Keyword(s):  
Group Structure ◽  
High Temperature Superconductors ◽  
Face Centered Cubic ◽  
Superconducting Transition ◽  
High Tc ◽  
Structure Search ◽  
Systematic Structure ◽  
Face Centered ◽  
Fcc Structure ◽  
Very High

A systematic structure search in the La–H and Y–H systems under pressure reveals some hydrogen-rich structures with intriguing electronic properties. For example, LaH10 is found to adopt a sodalite-like face-centered cubic (fcc) structure, stable above 200 GPa, and LaH8 a C2/m space group structure. Phonon calculations indicate both are dynamically stable; electron phonon calculations coupled to Bardeen–Cooper–Schrieffer (BCS) arguments indicate they might be high-Tc superconductors. In particular, the superconducting transition temperature Tc calculated for LaH10 is 274–286 K at 210 GPa. Similar calculations for the Y–H system predict stability of the sodalite-like fcc YH10 and a Tc above room temperature, reaching 305–326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very high-temperature superconductors.

Non-linear influence of hydrostatic pressure on the yielding of asymmetric anisotropic sheet metals

2016 ◽  
Vol 23 (2) ◽  
pp. 159-180
Author(s):  
Farzad Moayyedian ◽  
Mehran Kadkhodayan
Keyword(s):  
Hydrostatic Pressure ◽  
Potential Functions ◽  
Face Centered Cubic ◽  
Sheet Metals ◽  
Strength Differential ◽  
Plastic Potential ◽  
Yield Functions ◽  
Non Linear ◽  
Data Points ◽  
Face Centered

The objective of the current research is the investigation into possible non-linear influence of hydrostatic pressure on yielding of asymmetric (exhibiting the so-called “strength-differential effect”) anisotropic sheet metals. To reach this aim, two yield functions are developed, called here “non-linear pressure sensitive criteria I and II,” (NPC-1 and NPC-2). In addition, the non-associated flow rules are employed for these new criteria. The yield functions are defined as non-linearly dependent on hydrostatic pressure, while the plastic potential functions are introduced to be pressure insensitive. To calibrate these criteria, the yield functions need 10 directional experimental yield stresses and the plastic potential functions need eight Lankford coefficients data points. Four well-known anisotropic sheet metals with different structures, namely AA 2008-T4, a Face Centered Cubic material (FCC), AA 2090-T3, a Face Centered Cubic material (FCC), AZ31, a hexagonal closed packed material (HCP) and high-purity [Formula: see text]-titanium (HCP) are considered as case studies. Finally, it is observed that NPC-1 and NPC-2 are more successful than previous criteria in anticipating directional strength and mechanical properties.

scholarly journals Unconventional Co-Existence of Insulating Nano-Regions and Conducting Filaments in Reduced SrTiO3: Mode Softening, Local Piezoelectricity, and Metallicity

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 437
Author(s):  
Annette Bussmann-Holder ◽  
Hugo Keller ◽  
Arndt Simon ◽  
Gustav Bihlmayer ◽  
Krystian Roleder ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Carrier Concentration ◽  
Superconducting Transition Temperature ◽  
Superconducting Transition ◽  
First Principles Calculations ◽  
Effective Electron ◽  
Mode Softening ◽  
Component Type ◽  
Electron Phonon Coupling ◽  
Transverse Optic

Doped SrTiO3 becomes a metal at extremely low doping concentrations n and is even superconducting at n < 1020 cm−3, with the superconducting transition temperature adopting a dome-like shape with increasing carrier concentration. In this paper it is shown within the polarizability model and from first principles calculations that up to a well-defined carrier concentration nc transverse optic mode softening takes place together with polar nano-domain formation, which provides evidence of inhomogeneity and a two-component type behavior with metallicity coexisting with polarity. Beyond this region, a conventional metal is formed where superconductivity as well as mode softening is absent. For n ≤ nc the effective electron-phonon coupling follows the superconducting transition temperature. Effusion measurements, as well as macroscopic and nanoscopic conductivity measurements, indicate that the distribution of oxygen vacancies is local and inhomogeneous, from which it is concluded that metallicity stems from filaments which are embedded in a polar matrix as long as n ≤ nc.

Linear and Non-linear Polarizabilities for P2(X1Σg+)

1997 ◽  
Vol 52 (6-7) ◽  
pp. 564-566 ◽  
Author(s):  
George Maroulis
Keyword(s):  
Bond Length ◽  
Dipole Polarizability ◽  
Consistent Field ◽  
Electric Polarizabilities ◽  
Self Consistent ◽  
Non Linear ◽  
Self Consistent Field

Abstract Electric polarizabilities and hyperpolarizabilities were calculated from accurate self-consistent field wavefunctions for P2. The following values are reported, using the experimental bond length of 1.8934 Å: dipole polarizability αzz = 69.83 and αxx = 41.20 e2 a02 Eh-1 , second dipole hyperpolarizability γzzzz = 17 040, γxxxx= 11 581 and γxxzz = 4724 e4a04Eh-3, quadrupole polarizability, Czz „zz = 276.14, Cxz,xz = 232.64 and Cxx,xx = 151.25 e2 a04Eh-1 , dipole-octopole polarizability, Ez,zzz, = 331.00 and Ex,xxx = -154.66 e2 a04Eh-1 and for the dipole-dipole-quadrupole hyperpolarizability, Bzz,zz = - 2441, Bxz,xz = - 1442, Bxx,zz = 866 and Bxx,xx = - 1411 e3a04Eh-2.

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