Fermi surfaces in Nb<sub>3</sub>Sn through positron annihilation

Hoffmann, Ludger; Singh, Amreek; Takei, Hiroyuki; Toyota, Naoki

doi:10.1088/0305-4608/18/12/011

Cited by 16 publications

(9 citation statements)

References 28 publications

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“…It also suggests an explanation for why elements under high pressure are superconducting [64] for the fact that electron-doped cuprates have hole carriers in the regime where they become superconducting [65] and for the pervasive presence of hole carriers in superconducting materials ranging from the elements [66] to A15 compounds [67] to MgB 2 [68] to high-T c cuprates.…”

Section: Discussionmentioning

confidence: 99%

Effect of orbital relaxation on the band structure of cuprate superconductors and implications for the superconductivity mechanism

Hirsch

2014

Phys. Rev. B

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Where the doped holes reside in cuprate superconductors has crucial implications for the understanding of the mechanism responsible for their high-temperature superconductivity. It has been generally assumed that doped holes reside in hybridized Cu d x 2 −y 2 -O pσ orbitals in the CuO 2 planes, based on results of density functional band-structure calculations. Instead, we propose that doped holes in the cuprates reside in O pπ orbitals in the plane, perpendicular to the Cu-O bond, that are raised to the Fermi energy through local orbital relaxation, that is not taken into account in band-structure calculations that place the bands associated with these orbitals well below the Fermi energy. We use a dynamic Hubbard model to incorporate the orbital relaxation degree of freedom and find in exact diagonalization of a small Cu 4 O 4 cluster that holes will go to the O pπ orbitals for relaxation energies comparable to what is expected from atomic properties of oxygen anions. The bandwidth of this band becomes significantly smaller than predicted by band-structure calculations due to the orbital relaxation effect. Within the theory of hole superconductivity the heavy hole carriers in this almost full band will pair and drive the system superconducting through lowering of their quantum kinetic energy.

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Section: Discussionmentioning

confidence: 99%

Effect of orbital relaxation on the band structure of cuprate superconductors and implications for the superconductivity mechanism

Hirsch

2014

Phys. Rev. B

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“…25,26 The splitting of the ⌫ 12 doublet hardly affects the DOS at the Fermi level. 25,26 Taking the Fermi surface sheets obtained by the linear muffin-tin orbital method, which are supported by two-dimensional angular correlation of positron annihilation radiation in the cubic state, 50 we can exclude some sheets because their contribution to the DOS is too large. This is the case for bands Nos.…”

Section: Discussionmentioning

confidence: 99%

“…5 and 6 in the numbering adopted by Ref. 50, No. 5 containing the Fermi surface of a very flat band due to the Nb 4d electrons, assumed to be responsible for the high T c .…”

Section: Discussionmentioning

confidence: 99%

Specific heat ofNb3Sn: The case for a second energy gap

Guritanu

Goldacker²,

Bouquet

et al. 2004

Phys. Rev. B

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We present specific-heat data for Nb 3 Sn, a well-known technically applied superconductor with a critical temperature T c Х 18 K, in the temperature range from 1.2 to 200 K in zero magnetic field, and from 1.5 to 22 K in fields H ഛ 16 T. The particularly dense and homogeneous polycrystalline sample used for this study is characterized in detail. We determine the bulk upper critical field H c2 ͑T͒ from specific-heat data, and the Sommerfeld constant ␥ from the entropy S͑T͒. We investigate in detail a low-temperature anomaly already noticed in previous investigations in zero field, and find that this feature can be quantitatively ascribed to the presence of a second superconducting gap 2⌬ S ͑0͒Х0.8k B T c , in addition to the main one 2⌬ L ͑0͒Х4.9k B T c . The signature of this minor gap, which affects 7.5% of the electronic density-of-states, vanishes in high fields.

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“…Already with the A15 materials, (Nb 3 Sn, 109 as an important tool for Fermi surface studies in superconductors. There was a tremendous surge of activity following the discovery of high-temperature superconductivity in the cuprates, as discussed in the comprehensive review by Peter et al 112 One of the significant challenges encountered in the experiments on YBa 2 Cu 3 O 7 was the unavoidable (Coulombdriven) preference of the positron for the Cu-O chains over the Cu-O 2 planes.…”

Section: High-temperature Superconductorsmentioning

confidence: 99%