Fig. 4.

Line shape of the emission. Electromagnetic radiation at the washboard frequencies $f_0^{\left(2\right)}=10.02$ GHz at H = 3.15 T (a) and $f_0^{\left(1\right)}=19.96$ GHz at H = 4.2 T (b) for a vortex velocity v of 100 m s⁻¹ and a series of temperatures, as indicated. Symbols: experimental data; solid lines: Lorentz and Gauss fits. An offset of 0.5 is used along the vertical axis to facilitate reading the data. Inset in b: Temperature dependences of the normalized linewidth $\mathrm{\Delta }f\mathrm{∕}{f}_0^{\left(1,2\right)}$ at 3.15 T (triangles) and 4.2 T (circles)