  Chirality, i.e., the right- and left-handedness of structure, is one of the
key concepts in many fields of science including biology, chemistry and
physics, and its manipulation is an issue of vital importance. The electron
spins in solids can form chiral configurations. In perovskite manganites RMnO3
(R=Tb, Dy,...etc), the Mn-spins form a cycloidal structure, which induces
ferroelectric polarization (P) through the relativistic spin-orbit interaction.
This magnetism-induced ferroelectricity (multiferroics) and associated
infrared-active spin waves (electromagnons) open a promising route to control
the spins by purely electric means in a very short time. In this paper, we show
theoretically with an accurate spin Hamiltonian for TbMnO3 that a picosecond
optical pulse can switch the spin chirality by intensely exciting the
electromagnons with a terahertz frequency.
