Experimental Evidence for the Correlation-Produced Magnetoplasma Mode in Potassium

We have measured the real part of the surface impedance $R\left(H\right)\mathrm{}$ of potassium at 1.2°K in a magnetic field normal to the sample surface. We find a sharp peak in $R\left(H\right)\mathrm{}$ at the value of $H$ where Cheng, Clarke, and Mermin predicted a new correlation-produced magnetoplasma mode should exist. We interpret the peak in $R\left(H\right)\mathrm{}$ as confirmation of the existence of the mode, and we ascribe to surface roughness the overall variation in $R\left(H\right)\mathrm{}$.