  We have studied the structure of the superconducting gap in MgB2 thin films
by means of point-contact spectroscopy using a gold tip. The films were
produced by depositing pure boron on a sapphire substrate, using e-beam
evaporation, followed by reaction with magnesium vapour. The films have a Tc of
38.6 +- 0.3 K and resistivity of about 20 microOhm cm at 40 K. The
point-contact spectra prove directly the existence of a multi-valued order
parameter in MgB2, with two distinct values of the gap, DELTA1=2.3+-0.3 meV and
DELTA2=6.2+-0.7 meV at 4.2 K. Analysis of the spectra in terms of the
Blonder-Tinkham-Klapwijk model reveals that both gaps close simultaneously at
the Tc of the film. Possible mechanisms that can explain the intrinsic
co-existence of two values of the gap are discussed.
