Observation of Floquet topological corner and hinge states via higher-order topolectrical space-time circuits

Floquet higher-order topological insulators (HOTIs), hosting robust corner-/hinge-localized states under periodic driving, represent a pivotal frontier in nonequilibrium topological physics. Although theoretical studies suggest that nonsymmorphic space-time symmetries could stabilize exotic Floquet HOTIs, experimental realization—particularly in three dimensions—has remained elusive due to the fundamental challenge of dynamically coordinating spatial and temporal coupling modulations. Here we report an experimental demonstration of both two-dimensional (2D) and three-dimensional (3D) Floquet second-order topological states using spatiotemporal topolectrical circuits. Overcoming the inherent difficulties of precise spatiotemporal control in active circuits, we implement space-time-engineered modulations via voltage-controlled time-varying impedance converters with current inversion. This enables the engineering of nonsymmorphic space-time symmetry in circuit networks and the direct observation of topological corner/hinge dynamics within Floquet quasienergy gaps. Our methodology fundamentally surpasses the conventional paradigm in photonic and acoustic systems—where spatial-axis modulation mimics pseudotemporal drives—by achieving full, dynamically coordinated spatiotemporal governance of coupling trajectories, thereby enabling the experimental synthesis of high-dimensional higher-order Floquet topological matter.