Dynamical axion detection techniques

The unusual magnetoelectric transport present in Weyl semimetals and 3D topological insulators can be compactly understood as manifestations of a background axion field, which itself is determined by the microscopic band structure. In the presence of correlations, an additional axion quasiparticle may emerge as the collective excitations on top of the mean background field. Such modes couple nonlinearly to electric and magnetic fields, giving rise to a dynamical magnetoelectric response. However, unambiguous identification of this collective axion mode is challenging due to its inherent nonlinear dynamics. In this talk I will present recent work on axion detection techniques in condensed matter systems. The first is an all-optical detection protocol that utilizes a pump-probe setup for verifying and characterizing the transient dynamics of axion fields in three-dimensional insulator systems, with an optical signature manifesting in the time-dependent Kerr rotation. The second detection technique relies on use of a cross-resonator geometry specifically suited to detect time-reversal symmetry breaking, where the dynamics of the axion are embedded in the quantum metric.