  We report a temperature- and density-dependent decay of the 93mNb nuclear
excitation and give a minimal interpretation on the underlying physics. This
anomaly indicated nuclear resonant absorption as well as delocalization of the
long-lived Moessbauer state in the crystal. A nonlinear magnetoelectric
response, on low-frequency drive current, showed up in the bulk metal of a
high-purity niobium crystal and then disappeared with vanishing benchmarks of
delocalized nuclear excitation. Several nonlinear resonant peaks, on the order
of several hundreds of Hz, grew up with the applied magnetic field. The central
frequencies of these peaks decreased with temperature.
