Time refraction of spin waves

TL;DR

This paper experimentally demonstrates the phenomenon of time refraction in spin waves within microscopic waveguides, showing controllable frequency shifts and efficient energy conversion using strong magnetic field pulses.

Contribution

It introduces the first experimental observation of time refraction in spin waves, with a novel integrated design enabling high conversion efficiency and broadband frequency control.

Findings

Achieved up to 39% frequency conversion efficiency.

Demonstrated broadband and controllable spin-wave frequency shifts.

Excited spin-wave bursts with nanosecond pulse durations.

Abstract

We present an experimental study of time refraction of spin waves propagating in microscopic waveguides under the influence of time-varying magnetic fields. Using space- and time-resolved Brillouin light scattering microscopy, we demonstrate that the broken translational symmetry along the time coordinate can be used to in- or decrease the energy of spin waves during their propagation. This allows for a broadband and controllable shift of the spin-wave frequency. Using an integrated design of spin-wave waveguide and microscopic current line for the generation of strong, nanosecond-long, magnetic field pulses, a conversion efficiency up to 39% of the carrier spin-wave frequency is achieved, significantly larger compared to photonic systems. Given the strength of the magnetic field pulses and its strong impact on the spin-wave dispersion relation, the effect of time refraction can be quantified on a length scale comparable to the spin-wave wavelength. Furthermore, we utilize time refraction to excite spin-wave bursts with pulse durations in the nanosecond range and a frequency shift depending on the pulse polarity.