Electromagnons in the multiferroic state of perovskite manganites with symmetric-exchange striction

We have investigated electrically-active magnetic excitations (electromagnons) in perovskite manganites with the $E$-type (up-up-down-down) spin structure by terahertz spectroscopy. Eu${}_{1-x}$Y${}_x$MnO${}_3$ (0.1$\le x\le$1)andY$_{1-y}$Lu$_y$MnO$_3$(0$\le y\le$1)withoutmagnetic$f$-moments, which host collinear sinusoidal, $A$-type, cycloidal, and $E$-type spin orders, are used to examine the systematics of possible electromagnons. Three-peak structures (23, 35, 45 cm${}^{-1}$) of magnetic origin show up in the $E$-type phase with little composition ($y$) dependence of frequencies, making a contrast with the electromagnons observed in the cycloidal-spin ($x\le 0.8$) phases. One of these electromagnon is ascribed to the zone-edge magnon mode based on the calculated magnon dispersions.