The real-time observation of a coherent magnetic oscillation in NaV2O5

We studied the quantum spin ladder system, sodium vanadate, by using a femtosecond impulsive excitation technique and report on the first observation of the lattice and spin dynamics. We found a coherent magnetic oscillatory mode (magnon) at 127 cm−1(twice the spin gap energy) below TC (=34 K) with circularly polarized light, which means that the magnetic mode corresponds to a spin-flip excitation from the singlet ground state.