  Under hydrostatic pressure, the ground state of a two-dimensional electron
gas at $\nu=5/2$ changes from a fractional quantum Hall state to the stripe
phase. By measuring the energy gap of the fractional quantum Hall state and of
the onset temperature of the stripe phase we mapped out a phase diagram of
these competing phases in the pressure-temperature plane. Our data highlight
the dichotomy of two descriptions of the half-filled Landau level near the
quantum critical point: one based on electrons and another on composite
fermions.
