Ab initio calculations of H$_{c2}$ for Nb, NbSe2, and MgB2

Masao Arai; Takafumi Kita

doi:10.1143/JPSJ.73.2924

paper

Ab initio calculations of H $_{c 2}$ for Nb, NbSe2, and MgB2

arXiv:cond-mat/0404628 · doi:10.1143/JPSJ.73.2924

Abstract

We report on quantitative calculations of the upper critical field $H_{c 2}$ for clean type-II superconductors Nb, NbSe $_{2}$ , and MgB $_{2}$ using Fermi surfaces from {\em ab initio} electronic structure calculations. The results for Nb and NbSe $_{2}$ excellently reproduce both temperature and directional dependences of measured $H_{c 2}$ curves without any adjustable parameters, including marked upward curvature of NbSe $_{2}$ near $T_{c}$ . As for MgB $_{2}$ , a good fit is obtained for a $π / σ$ gap ratio of $\sim 0.3$ , which is close to the value from a first-principles strong-coupling theory [H. J. Choi \textit{et al}. Nature, \textbf{418} 758 (2002)]. Our results indicate essential importance of Fermi surface anisotropy for describing $H_{c 2}$ .

4 pages, 4 figures

Ab initio calculations of Hc2​ for Nb, NbSe2, and MgB2

Abstract

Ab initio calculations of H $_{c 2}$ for Nb, NbSe2, and MgB2