  We have performed Raman measurements on TbMnO3 single crystal under magnetic
field along the three crystallographic directions. The flip of the spin spiral
plane creates an electromagnon excitation. In addition to the electromagnons
induced by the Heisenberg coupling, we have detected the electromagnon created
by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified
all the vibrational modes of TbMnO3. Their temperature dependences show that
only one phonon observed along the polarization axis is sensitive to the
ferroelectric transition. This mode is tied to the Tb3+ ion displacements that
contribute to the ferroelectric polarization.
