  We have carried out a pressure study of the unconventional superconductor
FeTe0.6Se0.4 up to 1.5 GPa by neutron scattering, resistivity and magnetic
susceptibility measurements. We have extracted the neutron spin resonance
energy and the superconducting transition temperature as a function of applied
pressure. Both increase with pressure up to a maximum at ~1.3 GPa. This
analogous qualitative behavior is evidence for a correlation between these two
fundamental parameters of unconventional superconductivity. However, Tc and the
resonance energy do not scale linearly and thus a simple relationship between
these energies does not exist even in a single sample. The renormalization of
the resonance energy relative to the transition temperature is here attributed
to an increased hybridization. The present results appear to be consistent with
a pressure-induced weakening of the coupling strength associated with the
fundamental pairing mechanism.
