Onset of spin wave time-domain fractals in a dynamic artificial crystal

摘要

We report on the first observation of an exact fractal pattern in the time-domain arising spontaneously from a dynamic artificial crystal (DAC). The all-magnon process occurs in a passive, unlithographed magnetic wave-guide. The DAC was created by a standing spin wave of frequency f(DAC) in a region of nonlinear waveguide, resulting in a spatio-temporally periodic potential. The interaction of travelling spin waves of frequency f' with the DAC resulted in a series of new modes appearing in a comb with intervals Delta f((0)) = vertical bar f(DAC) - f'vertical bar. As the magnetic field H was increased a 1st pre-fractal pattern was observed with frequency interval Delta f((1)) = Delta f((0))/2. Finally, the onset of a 2nd pre-fractal was observed with frequency interval Delta f((2)) = Delta f((1))/2 = Delta f((0))/4. The magnetic field dependence of the nonlinear signals matched that of the DAC. The spin wave fractal behavior was demonstrated for different values of f'.