Intrinsic type-2 superconductivity in pure niobium

✍ Scribed by R.A. French

• Publisher: Elsevier Science
• Year: 1968
• Tongue: English
• Weight: 701 KB
• Volume: 8
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/s0011-2275(68)80007-4

✦ Synopsis

Accurate magnetization experiments on niobium (F > 2000) from the superconducting transition temperature of 9.20(+_ O.03)°K to 1.5°K produced highly reversible curves. D.c. resistance measurements~ yielding He3/He2 ratios of 3.4 to 3.65--suggest this to be partly due to poor surface finish.

Temperature change altered the shape of the magnetization curves, which displayed a discontinuity in dM/dH at 1.005He~ and continuous non-linear approach to M = 0 at He2. Data were consistent with a ).-transition at Hep Thermodynamic critical fields He(t) obeyed the parabolic law, indicating strong coupling: 2~(0) was 3.67(+ 0.05) kTc.

Nearer Te, the energy gap followed the BCS expression

for B=3.9(+0.2). Other o o parameters were ~o = 390(+_ 15)A, ).L(O) = 333(+ 15)A, S/St = 0.79, and Ko = 0.815(+-0.015). The Maki functions Kl(t), K2(t) were in fair accord With theory, but changed rapidly with temperature, KI(O)[K(1) being 1.68, 30% too high. This discrepancy is not explained in non-local corrections to GLAG theory.