Enhancement of Nuclear Magnetic Resonance in Bulk Rubidium in the Size-Effect Regime

The intensity of nuclear magnetic resonance absorption of ${\mathrm{Rb}}^{87}$ nuclei in a thin slab of purified, cooled metal is observed to increase significantly in the range of magnetic-field strength and orientation where nearly sinusoidal size-effect variations in the surface resistance are found. Though no quantitative description of the effect is presently available, it clearly results from enhanced penetration of radio-frequency currents and fields into the bulk of the metal slab due to the cyclotron motion of the electrons. The phenomenon is expected to be generally observable in pure metals at low temperatures.