Pressure dependence of the upper critical field of MgB2 and of YNi2B2C

H. Suderow; V. G. Tissen; J. P. Brison; J. L. Martinez; S. Vieira; P. Lejay; S. Lee; S. Tajima

doi:10.1103/PhysRevB.70.134518

paper

Pressure dependence of the upper critical field of MgB2 and of YNi2B2C

arXiv:cond-mat/0412042 · doi:10.1103/PhysRevB.70.134518

Abstract

We present measurements of H $_{c 2} (T)$ under pressure in MgB $_{2}$ and in YNi $_{2}$ B $_{2}$ C. The changes in the shape of H $_{c 2} (T)$ are interpreted within current models and show the evolution of the main Fermi surface velocities $v_{F}$ and electron-phonon coupling parameters $λ$ with pressure. In MgB $_{2}$ the electron-phonon coupling strength of the nearly two dimensional $σ$ band, responsible for the high critical temperature, is more affected by pressure than the $π$ band coupling, and the hole doping of the $σ$ band decreases. In YNi $_{2}$ B $_{2}$ C, the peculiar positive curvature of H $_{c 2} (T)$ is weakened by pressure.

5 pages, 5 figures