Low-frequency subharmonics in the turbulent spectrum on the surface of liquid hydrogen

Two-dimensional wave turbulence on the charged surface of liquid hydrogen in a rectangular cell has been studied. It has been found that, after intense monochromatic pumping at frequencies of $14$–$30$ Hz in an electric field partially compensating the gravitational field of the Earth, incommensurate subharmonics at low frequencies until $0.8$ Hz can be observed on the surface of the liquid with a certain time delay in addition to the direct turbulent cascade of Kolmogorov–Zakharov capillary waves. The nonlinear interaction of these subharmonics with each other and with a wave excited at the pump frequency results in the appearance of additional combination waves in the direct turbulence spectrum.