Directional Excitation of a High-Density Magnon Gas Using Coherently Driven Spin Waves
Brecht G. Simon (TU Delft - QN/vanderSarlab, Kavli institute of nanoscience Delft, TU Delft - QN/Quantum Nanoscience)
Samer Kurdi (TU Delft - QN/Quantum Nanoscience, Kavli institute of nanoscience Delft, TU Delft - QN/vanderSarlab)
Helena La (External organisation)
Iacopo Bertelli (Universiteit Leiden, TU Delft - QN/Quantum Nanoscience, Kavli institute of nanoscience Delft, TU Delft - QN/vanderSarlab)
Joris J. Carmiggelt (TU Delft - QN/Quantum Nanoscience, Kavli institute of nanoscience Delft, TU Delft - QN/vanderSarlab)
Maximilian Ruf (TU Delft - QID/Hanson Lab)
Nick De Jong (TNO, TU Delft - QuTech Advanced Research Centre, TU Delft - BUS/TNO STAFF)
Hans Van Den Berg (TU Delft - QuTech Advanced Research Centre, TU Delft - Business Development, TNO)
Allard J. Katan (TU Delft - QN/Quantum Nanoscience, TU Delft - QN/Afdelingsbureau, Kavli institute of nanoscience Delft)
Toeno Van Der Sar (Kavli institute of nanoscience Delft, TU Delft - QN/vanderSarlab, TU Delft - QN/Quantum Nanoscience)
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Abstract
Controlling magnon densities in magnetic materials enables driving spin transport in magnonic devices. We demonstrate the creation of large, out-of-equilibrium magnon densities in a thin-film magnetic insulator via microwave excitation of coherent spin waves and subsequent multimagnon scattering. We image both the coherent spin waves and the resulting incoherent magnon gas using scanning-probe magnetometry based on electron spins in diamond. We find that the gas extends unidirectionally over hundreds of micrometers from the excitation stripline. Surprisingly, the gas density far exceeds that expected for a boson system following a Bose-Einstein distribution with a maximum value of the chemical potential. We characterize the momentum distribution of the gas by measuring the nanoscale spatial decay of the magnetic stray fields. Our results show that driving coherent spin waves leads to a strong out-of-equilibrium occupation of the spin-wave band, opening new possibilities for controlling spin transport and magnetic dynamics in target directions.
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