  We report high-resolution specific heat data on a high-quality single crystal
of the classical superconductor V3Si, which reveal tiny lambda-shape anomalies
appearing superimposed onto the BCS specific heat jump at the superconducting
transition in magnetic fields of 2 T and higher. The appearance of these
anomalies is accompanied by a magnetic-field-induced broadening of the
superconducting transition. We demonstrate, using scaling relations predicted
by the fluctuation models of the 3d-XY and the 3d-Lowest-Landau-Level (3d-LLL)
universality class, that the effect of critical fluctuations becomes
experimentally observable due to of a magnetic field-induced enlargement of the
regime of critical fluctuations. The scaling indicates that a reduction of the
effective dimensionality due to the confinement of quasiparticles into low
Landau levels is responsible for this effect.
