Upper critical magnetic fields Hc2(T) have been measured resistively for the high‐temperature (Tc≳90 K) superconductors TmBa2Cu3O9−δ and YBa2Cu3O9−δ in applied magnetic fields H up to 9 T. If H at the resistive midpoint is defined as Hc2, then the upper critical field slopes (dHc2/dT)Tc at the superconducting transition temperatures Tc are respectively −2.8 and −1.1 T/K. The Tm‐specimen initial slope is apparently the highest yet reported for 90 K superconductors. Extrapolations from this slope, based on standard, three‐dimensional, dirty‐limit Werthamer, Helfand, Hohenberg, and Maki theory, yield (1) zero‐temperature upper critical fields Hc2(T=0)=99–175 T, where the range is determined by the degree of paramagnetic limitation; (2) Hc2(T=77 K)≊36 T, the upper critical field at the boiling point of liquid nitrogen.
Thulium barium copper oxide: A 90‐K superconductor with a potential 1‐MG upper critical field
J. J. Neumeier, Y. Dalichaouch, J. M. Ferreira, R. R. Hake, B. W. Lee, M. B. Maple, M. S. Torikachvili, K. N. Yang, H. Zhou; Thulium barium copper oxide: A 90‐K superconductor with a potential 1‐MG upper critical field. Appl. Phys. Lett. 3 August 1987; 51 (5): 371–373. https://doi.org/10.1063/1.98445
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