Magnetic field induced one-magnon Raman scattering in the magnon Bose-Einstein condensation phase of TlCuCl3

We report the observation of the A(g)-symmetric one-magnon Raman peak in the magnon Bose-Einstein condensation phase of TlCuCl(3). Its Raman shift traces the one-magnon energy at the magnetic Gamma point, and its intensity is proportional to the squared transverse magnetization. The appearance of the one-magnon Raman scattering originates from the exchange magnon Raman process and reflects the change of the magnetic-state symmetry. By using the bond-operator representation, we theoretically clarify the Raman selection rules, which are consistent with the experimental results.