Three-dimensional collective flux pinning in the layered superconductor 2H-NbSe2-xSx

The collective pinning theory was compared with the results of flux pinning in the layered superconductor 2H-NbSe _2–x S _x.The size effect on the flux-pinning force and the angular dependence of the peak effect were investigated. Our sample did not show the size effect. Even when a magnetic field was applied parallel to the crystal layers, the peak effect was observed far below the zero-field critical temperature. These results show that flux pinning is three-dimensional within the frame of the collective pinning theory and that the peak effect is not caused by the dimensional crossover. The peak effect can be qualitatively explained in terms of the dispersion of the tilt modulus of the flux-line lattice.