Effect of strong magnetic fields on superconducting transition of single-crystal NbSe2

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Abstract
The transition temperature of a composite of five single crystals of NbSe2 was measured as a function of magnetic field with the crystal layers in both the parallel and perpendicular orientations with respect to the applied field. Plots of Hc2 versus T for both orientations yielded straight lines up to the largest applied fields of approximately 90 kOe. Linear extrapolation of these lines to T = 0 results in intercepts of the Hc2 axis at 167 and 57.7 kOe for the parallel and perpendicular orientation, repectively. The respective slopes for the parallel and perpendicular orientation are 23.3 and 7.82 kOe/K. The transition temperature in zero applied field was found to be 7.27 K. The transition curves in applied fields exhibited long ``tails'' due to microscopic and macroscopic misalignments of parts of the layer structure with respect to the field. Transverse magnetization measurements near Tc yielded Hc and (d Hc/d t)t = 1 as well as the Ginzburg‐Landau parameters κ1(Tc)≃10.6±10% and κ2(Tc)≃11.2±4% for 6 K < T < Tc. Using the tunneling data for the transverse energy gap Δ(0) in the Toxen relation Δ(0)/k Tc = [Hc (0)]−1(dHc/dt)t = 1, Hc(0) was found to be 2.04 kOe±10%. This agreed well with extrapolations of Hc versus t2 plots which yielded Hc(0)=1.95 kOe±10%. Comparisons are made for high‐field data obtained on other samples from our laboratory and others. There is evidence for a slight positive curvature in the Hc2 versus T characteristic near Tc for the parallel field orientation of our samples.