  We study the four-dimensional Yang-Mills theory in the presence of a
three-dimensional membrane of fermions by lattice Monte Carlo simulations. We
analyze the phase structure of this theory at finite temperature. Below the
phase transition temperature of the pure Yang-Mills theory, we obtain an
unconventional phase with spatially-nonuniform vacuum. In this phase, the
expectation value of the Polyakov loop is finite on the membrane, and it
exponentially decays to zero outside the membrane.
