對雙能隙超導體砷化鈮的理論研究

Theoretical Study on NbSe2 as a Two-gap Superconductor

柯達(Ta Ko)

指導教授 ： 高英哲

國立臺灣大學/理學院/物理研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.03415

摘要

無資料

關鍵字

鈮化砷 ； 雙能隙 ； 硼化錳 ； 超流體密度 ； 較高臨界場

並列摘要

NbSe2 has been recognized as a multiband superconductor recently by many experiments, including
the reported Fermi-sheet-dependent superconductivity in angle-resolved photoemission
spectroscopy, thus strongly suggesting the multiband nature in NbSe2. It appears that a second
energy gap involved can give a plausible explanation for previous experiments. Viewing NbSe2
as a two-gap superconductor, we proposed two possible scenarios to investigate how to locate
the large gap and the small gap on the three bands in NbSe2. The two-gap Ginzburg-Landau
theory is used to calculate the upper critical field and the corresponding gap ratio near Tc. Also,
we apply the two-band Eilenberger equations and the two-gap BCS theory to calculate the superfluid
density and the specific heat. The obtained results are fitted to previous experimental
data, and it appears that the more plausible scenario is to respectively locate the large gap
and the small gap on Nb-derived antibonding band and the Nb-derived bonding band. While
previous studies have suggested that the Se-derived band serves as the isotropic small gap, we
exclude such role of the Se-derived band for two reasons. One is its bad fit to the superfluid
density, and the other is that the gap ratio obtained in the fit to Hc2(ab) is inconsistent with
previous ARPES studies. Additionally, we discuss how the upper critical field is affected by
the intraband Fermi-velocity anisotropy, interband Fermi-velocity anisotropy, density of states,
interband coupling and the transition temperature of the large gap.

並列關鍵字

two-gap ； Ginzburg-Landau theory ； Eilenberger equation ； NbSe2 ； MgB2 ； Superfluid density ； upper critical field

參考文獻

[26] C.L. Huang, J.Y. Lin, Y.T. Chang, C.P. Sun, H.Y. Shen, C.C. Chou, H. Berger, T.K. Lee,

[53] F. Bouquet, Y. Wang, R. A. Fisher, D. G. Hinks, J. D. Jorgensen, A. Junod, and N. E.

Rev. Lett. 87, 167003 (2001).

W. Weber, Phys. Rev. B 66, 052505 (2002).

014504 (2002).