Experimental study of the surface properties of superfluid and normal ³He by plasma resonance of Wigner solid

A new experimental method has been developed for using plasma resonance of Wigner solid (WS) for the study of liquid 3He surface properties in superfluid and normal states. The behaviour of optical coupled plasmon-ripplon (CPR) resonances have been investigated in magnetic field 15 mT at temperatures down to 0.35 mK. The position of transverse optical plasma mode, which becomes visible when weak magnetic field is applied gives the information about WS coupling with helium surface. The line width of CPR resonance is used for getting the collision time in the scattering of surface electrons from the surface roughness. The influence of the superfluid transition on the collision time is observed.