Superconducting Properties of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow><mml:mi mathvariant="normal">M</mml:mi><mml:mi mathvariant="normal">g</mml:mi><mml:mi mathvariant="normal">B</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>from First Principles

Floris, Andrea; Profeta, G.; Lathiotakis, N. N.; Lüders, M.; Marques, Miguel A. L.; Franchini, Cesare; Gross, E. K. U.; Continenza, A.; Massidda, S.

doi:10.1103/physrevlett.94.037004

Cited by 146 publications

(118 citation statements)

References 40 publications

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“…49 The data for T Յ 2 K vary among these groups, most likely reflecting experimental limitations. We note also that first-principles calculations based on a presumed s-wave -gap symmetry 14,51 do not agree well with the data in the 2 Յ T Յ 10 K temperature domain. Hence, we interpret these specific-heat measurements and calculations to be consistent with nodal lines.…”

Section: Relation Of Our Findings To Existing Literaturementioning

confidence: 77%

Evidence for non-s-wave symmetry of theπgap inMgB2from intermodulation distortion measurements

Agassi

Oates

Moeckly³

2009

Phys. Rev. B

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We present low-temperature low-power intermodulation-distortion ͑IMD͒ measurements of high-quality MgB 2 thin films that are inconsistent with presumed s-wave symmetry of the order parameter. The measurements were carried out in a stripline resonator at approximately 2 GHz between 1.8 K and T c . The IMD arises from the nonlinear Meissner effect in which the penetration depth is dependent on the RF magnetic field. Specifically, the observed IMD vs temperature T for T Ӷ T c / 2 varies as T −2 , while for an s-wave gap symmetry in the clean limit, the low-temperature IMD decreases exponentially with decreasing temperature. We calculate the IMD from first principles for different order-parameter symmetries using a Green's function approach and compare the results with the measured data. We propose that the observed upturn in the low-temperature IMD implies an admixture of an order parameter with nodal lines into the energy gaps of MgB 2 . Most likely, this admixture is prominent for the gap. Within the constraints of the hexagonal crystal symmetry of MgB 2 , the best fit with our IMD measurements is obtained with a gap ⌬͑ , T͒ = ⌬ 0 ͑T͒sin͑6͒, where is the azimuthal angle in the ab plane, and ⌬ 0 ͑T͒ is the amplitude, weakly temperature dependent at low temperatures. This gap symmetry entails six nodal lines. We also present low-temperature penetration-depth measurements that are consistent with the proposed nodal gap symmetry. To relate our proposition with existing literature, we review other low-temperature probes of the order-parameter symmetry. The literature presents conflicting results, some of which are in direct support of the symmetry proposed here.

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Section: Relation Of Our Findings To Existing Literaturementioning

confidence: 77%

Evidence for non-s-wave symmetry of theπgap inMgB2from intermodulation distortion measurements

Agassi

Oates

Moeckly³

2009

Phys. Rev. B

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“…Within the class of conventional (meaning phonon-driven) SC, density functional theory for the SC state (SCDFT) [9], within the available functional [10,11], proved to be predictive and reliable [12][13][14][15][16][17][18][19][20][21]. However, since the pairing in the pnictides and cuprates is nonphononic [22,23], this SCDFT approach is not directly applicable, due to the limitations of the functional.…”

Section: Introductionmentioning

confidence: 99%

Superconducting pairing mediated by spin fluctuations from first principles

et al. 2014

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We present the derivation of an ab initio and parameter-free effective electron-electron interaction that goes beyond the screened random phase approximation and accounts for superconducting pairing driven by spin fluctuations. The construction is based on many-body perturbation theory and relies on the approximation of the exchange-correlation part of the electronic self-energy within time-dependent density functional theory. This effective interaction is included in an exchange-correlation kernel for superconducting density functional theory in order to achieve a completely parameter free superconducting gap equation. First results from applying the new functional to a simplified two-band electron gas model are consistent with experiments.

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“…2,3,4 It would be of great interest to quantify this effect within the ab initio approach. 15 Note, that the σπ plasmon does not influence inter-band σ-π and intra-band σ scattering due to the phase-space restrictions, although could have some effect in the intra-band π one.…”

mentioning

confidence: 99%

“…In particular, in all evaluations of the e−ph interaction the adiabatic approximation has been used, and even in ab initio calculations 15 of T c the dynamical Coulomb interaction has been considered in its static form. Here we present a detailed ab initio study of the low-energy dynamical electronic properties of MgB 2 .…”

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confidence: 99%

Ab initiocalculation of low-energy collective charge-density excitations inMgB2

et al. 2009

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We present ab-initio time-dependent density-functional theory calculation results for low-energy collective electron excitations in MgB 2 . The existence of a long-lived collective excitation corresponding to coherent charge density fluctuations between the boron σ-and π-bands (σπ mode) is demonstrated. This mode has a sine-like oscillating dispersion for energies below 0.5 eV. At even lower energy we find another collective mode (σσ mode). We show the strong impact of local-field effects on dielectric functions in MgB2. These effects account for the long q-range behavior of the modes. We discuss the physics that these collective excitations bring to the energy region typical for lattice vibrations.PACS numbers: 74.25. Kc,71.45.Gm,73.43.Lp,74.70.Ad After several years of intense experimental and theoretical study of the origin of unusually high temperature superconductivity 1 in MgB 2 , nowadays there is a general belief that the superconductivity in MgB 2 is phonon-mediated with multiple gaps and an exceptional role played by E 2g phonon mode in strong coupling to electrons in the tubular-shaped σ bands at the Fermi level, E F . However, despite the tremendous progress achieved in understanding of superconductivity in MgB 2 , many of its fundamental properties related to phonons and electron-phonon (e − ph) coupling are still puzzling and remain under intense debate. Thus such important issues as, e.g., the reduced isotope effect, 2,3,4 the nature of the strong broad continuum in Raman spectra, the unusually broad linewidth of the E 2g phonon mode seen in Raman spectra, 5,6,7 the inconsistency between the results of Raman scattering and x-ray measurements, 8,9,10 and the role of non-adiabatic effects 8,11,12,13,14 have not yet found satisfactory explanations.As for the electronic part of the e−ph picture of superconductivity in MgB 2 , it has received substantially less attention than the phonon part. In particular, in all evaluations of the e−ph interaction the adiabatic approximation has been used, and even in ab initio calculations 15 of T c the dynamical Coulomb interaction has been considered in its static form. Here we present a detailed ab initio study of the low-energy dynamical electronic properties of MgB 2 . We demonstrate that the strongly anisotropic electronic structure of MgB 2 characterized by boron quasi two-dimensional σ and three-dimensional π bands 16,17 leads to remarkable low-energy dielectric response in this compound: collective modes with a peculiar sine-like oscillating dispersion appear in the 0-0.5 eV energy range. This brings interesting physics to the energy region which was thought to be entirely dominated by lattice vibrations.Our approach is based on time-dependent density functional theory 18 where the non-local dynamical densityresponse function, χ, determines an induced charge density, ρ, in the electronic system caused by an external potential, υ ext , according toχ is obtained from the integral equationis the response function of non-interacting electron system, υ(r − r ...

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Superconducting Properties ofMgB2from First Principles

Cited by 146 publications

References 40 publications

Evidence for non-s-wave symmetry of theπgap inMgB2from intermodulation distortion measurements

Evidence for non-s-wave symmetry of theπgap inMgB2from intermodulation distortion measurements

Superconducting pairing mediated by spin fluctuations from first principles

Ab initiocalculation of low-energy collective charge-density excitations inMgB2

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