Search Results for « Magnetophononics »

Abstract The direct, ultrafast excitation of polar phonons with electromagnetic radiation is a potent strategy for controlling the properties of a wide range of materials, particularly in the context of influencing their magnetic behavior. Here, we show that, contrary to common perception, the origin of phonon-induced magnetic activity does not stem from the Maxwellian fields resulting from the motion of the ions themselves or the effect their motion exerts on the electron subsystem. Through the mechanism of electron–phonon coupling, a coherent state of circularly polarized phonons generates substantial non-Maxwellian fields that disrupt time-reversal symmetry, effectively emulating the behavior of authentic magnetic fields. Notably, the effective fields can reach magnitudes as high as 100 T, surpassing by a factor of α−2≈2×104 the Maxwellian fields resulting from the inverse Faraday effect; α is the fine-structure constant. Because the light-induced nonreciprocal fields depend on the square of the phonon displacements, the chirality the photons transfer to the ions plays no role in magnetophononics.

One route to the control of quantum magnetism at ultrafast timescales is magnetophononics, the modulation of magnetic interactions by coherently driven lattice excitations. Theoretical studies of a gapped quantum magnet subject to continuous, single-frequency driving of one strongly coupled phonon mode find intriguing phenomena including mutually repelling phonon-bitriplon excitations and global renormalization of the spin excitation spectrum. Because experiments are performed with ultrashort pulses that contain a wide range of driving frequencies, we investigate phonon-bitriplon physics under pulsed laser driving. We use the equations of motion to compute the transient response of the driven and dissipative spin-phonon system, which we characterize using the phonon displacement, phonon number, and triplon occupations. In the Fourier transforms of each quantity we discover a low-frequency energetic oscillation between the lattice and spin sectors, which is an intrinsically nonequilibrium collective mode, and demonstrate its origin as a beating between mutually repelling composite excitations. We introduce a phonon-bitriplon approximation that captures all the physics of hybridization, collective mode formation, and difference-frequency excitation, and show that sum-frequency phenomena also leave clear signatures in the response. We model the appearance of such magnetophononic phenomena in the strongly coupled spin-chain compound CuGeO 3 , whose overlapping phonon and spin excitation spectra are well characterized, to deduce the criteria for their possible observation in quantum magnetic materials.