Broad-wave-vector spin pumping of flat-band magnons

We report the experimental observation of large spin -pumping signals in the YIG/Pt system driven by broad -wave -vector spin -wave spin current. 280-nm-wide microwave inductive antennas offer broad -wavevector excitation, which, in combination with the quasiflatband of YIG, allows a large number of magnons to participate in spin pumping at a given frequency. Through comparison with ferromagnetic resonance spin pumping, we attribute the enhancement of the spin current to the multichromatic magnons. The high efficiency of spin -current generation enables us to uncover nontrivial propagating properties in ultralow power regions. Additionally, our study achieves the spatially separated detection of magnons, allowing the direct extraction of the decay length. The synergistic combination of the capability of broad -wavevector excitation, enhanced voltage signals, and nonlocal detection provides an alternative avenue for the electrical exploration of spin -wave dynamics.