Fig. 2.

Microwave emission from Abrikosov vortices in the Mo/Si superlattice. a–e Emission spectra for a series of vortex velocities v, as indicated, at H = 3.15 and 4.2 T and T = 1.8, 3.0, and 3.6 K. The symbols above the emission peaks indicate the frequencies f_m = mf₀, which are harmonically related to the washboard frequency $f_0^{\left(1\right)}$ associated with the 50 Å-periodic layered structure (triangles) and $f_0^{\left(2\right)}$ related to the 100 Å-spaced vortex rows in the direction of their motion (circles). The odd and even harmonics are indicated by solid and open symbols, respectively. The vortex lattice configurations, which are commensurate with the Mo/Si multilayer period at $H_{N=2}^{\left(2\right)}=3.15$ T with $a^{\left(2\right)}=2d^{\left(2\right)}\mathrm{∕}\sqrt{3}=4s\mathrm{∕}\sqrt{3}$ and $H_{N=1}^{\left(1\right)}=4.2$ T with a⁽¹⁾ = 2d⁽¹⁾ = 2s, are shown in the scaled coordinate system (γa, c) above the panels. In the absence of transport current, vortices are centered in regions of reduced order parameter, the Si layers. The size of the circles denoting the vortex cores (not to scale) reflects their relation to the Si layer thickness d_Si and the multilayer period s