Anisotropic Eliashberg theory of MgB2: Tc, isotope effects,superconducting energy gaps, quasiparticles, and specific heat

Journal Article · Mon Jul 01 04:00:00 EDT 2002 · Physica C

OSTI ID:881599

edu, sglouie@uclink berkeley

The anisotropic Eliashberg formalism, employing results from the ab initio pseudopotential density functional calculations, is applied to study the superconducting properties of MgB2. It is shown that the relatively high transition temperature of MgB2 originates from strong electron-phonon coupling of the hole states in the boron sigma-bonds although the coupling strength averaged over the Fermi surface is moderate, and the reduction of the isotope effect arises from the large anharmonicity of the relevant phonons. The superconducting energy gap is nodeless but its value varies strongly on different pieces of the Fermi surface. The gaps a values delta(k) cluster into two groups at low temperature, a small value of approximately 2 meV and a large value of approximately 7 meV, resulting in two thresholds in the quasiparticle density of states and an increase in the specific heat at low temperature due to quasiparticle excitations over the small gap. All of these results are in good agreement with corresponding experiments and support the view that MgB2 is a phonon-mediated multiple-gap superconductor.

• Research Organization: Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Office of Basic EnergySciences; National Science Foundation Grant DMR 00-87088; MillerInstitute for Basic Research in Science
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 881599
• Report Number(s): LBNL--52473; BnR: KC0202030
• Journal Information: Physica C, Journal Name: Physica C Vol. 385
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BORON
ELECTRON-PHONON COUPLING
ENERGY GAP
FERMI LEVEL
FUNCTIONALS
ISOTOPE EFFECTS
PHONONS
SPECIFIC HEAT
TRANSITION TEMPERATURE
multi-gap superconductivity band structure isotope effectspecific heat phonosEliashberg theory Fermi surface