We report the observation of intermittency in gravity-capillary wave turbulence on the surface of mercury. We measure the temporal fluctuations of surface wave amplitude at a given location. We show that the shape of the probability density function of the local slope increments of the surface waves strongly changes across the time scales. The related structure functions and the flatness are found to be power laws of the time scale on more than one decade. The exponents of these power laws increase nonlinearly with the order of the structure function. All these observations show the intermittent nature of the increments of the local slope in wave turbulence. We discuss the possible origin of this intermittency.PACS numbers: 47.35.-i, 47.52.+j, 05.45.-a One of the most striking feature of turbulence is the occurrence of bursts of intense motion within more quiescent fluid flow. This generates an intermittent behavior [1,2]. One of the quantitative characterization of intermittency is given by the probability density function (PDF) of the velocity increments between two points separated by a distance r. Starting from a roughly Gaussian PDF at integral scale, the PDFs undergo a continuous deformation when r is decreased within the inertial range and develop more and more stretched exponential tails [3]. Deviation from the Gaussian shape can be quantified by the flatness of the PDF. The origin of nonGaussian statistics in three dimensional hydrodynamic turbulence has been ascribed to the formation of strong vortices since the early work of Batchelor and Townsend [1]. However, the physical mechanism of intermittency is still an open question that motivates a lot of studies in three dimensional turbulence [4]. Intermittency has been also observed in a lot of problems involving transport by a turbulent flow for which the analytical description of the anomalous scaling laws can be obtained [5].It has been known since the work of Zakharov and collaborators that weakly interacting nonlinear waves can also display Kolmogorov type spectra related to an energy flux cascading from large to small scales [6,7]. These spectra have been analytically computed using perturbation techniques, but can also be obtained by dimensional analysis using Kolmogorov-type arguments [8]. More recently, it has been proposed that intermittency corrections should be also taken into account in wave turbulence [9] and may be connected to singularities or coherent structures [8,10] such as wave breaking [11] or whitecaps [8] in the case of surface waves. However, intermittency in wave turbulence is often related to non Gaussian statistics of low wave number Fourier amplitudes [10], thus it is not obviously related to small scale intermittency of hydrodynamic turbulence. Surprisingly, there exist only a small number of experimental studies on wave turbulence [12,13,14,15,16] compared to hydrodynamic turbulence, and to the best of our knowledge, no experimental observation of intermittency has been reported in wave turbulence.In this letter, we repo...

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PACS. 46.10.+z Mechanics of discrete systems - 83.70.Fn Granular solids,