Time Refraction of Spin Waves

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, nanosecondlong, 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.

Photonics of time-varying media

“…This is particularly challenging due to the need for modulating a medium on a temporal scale similar to the optical frequency of the light field. Time-varying effects have been demonstrated in mechanical, 206 magnetic, 207 acoustooptic, 208 opto-mechanical, 209 and electronic systems. 133 In particular, electromagnetic metasurfaces can be modulated via mechanical actuation, chemical reactions, or phase-change materials, as well as electrically.…”

Phonon transport in the gigahertz to terahertz range: Confinement, topology, and second sound

“…Such time-resolved measurements are useful for studying phase transitions, for instance glass transitions 68 . Beyond pulsed lasers, time-resolved BLS be combined with other external stimuli, such as magnetic fields for studying spin waves 69 . An interesting task for timeresolved BLS will be to examine the elastic properties of 2D materials with interesting topological properties and photoinduced phase transitions like MoSe 2 70 , MoTe 2 71 and WTe 2 72 .…”

Numerical reverse engineering of general spin-wave dispersions: Bridge between numerics and analytics using a dynamic-matrix approach

“…One of the standard magnetic elements considered in various spin-wave transport experiments is the transversallymagnetized rectangular waveguide. [47][48][49][50] Here, we consider a soft-magnetic waveguide of 800 nm width and 50 nm thickness shown in Fig. 2 The waveguide is magnetized in an S state which is stabilized by a static transversal field of µ 0 H ext = 50 mT.…”

“…8 by numerically determining the magnetic ground state and then extracting approximate values for the effective magnetic field and the effective width of the waveguide. 49,50…”