Electromagnon H-T phase diagram of multiferroic TbMn$_2$O$_5$

We report the results of infrared (5--250 cm$^{-1}$) transmission study of multiferroic TbMn$_2$O$_5$ as a function of temperature (3--300~K) and H$\|$a for magnetic fields up to 8 T. Our major observation is that the main electromagnon feature softens without splitting with increasing field at T=5 K. This observation is in contrast with the gradual suppression of electromagnons without shifting by magnetic field in RMnO$_3$ compounds. Also, it is in agreement with the theoretical prediction of Fang and Hu \footnote{C. Fang and J. Hu, condmat/0703487} for this system. In this talk, we will also discuss other features of the magnetic field dependence of the low energy electromagnon excitations in multiferroic TbMn$_2$O$_5$.