A-B TRANSITION OF SUPERFLUID HE-3 WITH A FILM GEOMETRY

We have performed cw NMR experiments on superfluid He-3 confined to a parallel-plate geometry with a mu m scale spacing for a wide pressure range. A static field was applied parallel or perpendicular to the pla te surface. The spectra of two absorption signals, a main and a satell ite, have been observed below the superfluid transition temperature in a parallel field. As the temperature decreased the main signal decrea sed with shifts to higher frequencies, and the satellite grew with shi fts to much higher frequencies. From the temperature dependence of the se signals and the result in the perpendicular field, it is confirmed that the main signal and the satellite correspond to the A phase signa l (ABM state) and the B phase signal (BW state), respectively. The tem perature dependence of the two signals indicates that a phase transiti on from the A phase to the B phase occurs with decreasing temperature. By analyzing these signals, we determine A-B transition temperatures experimentaly. The A-B transition temperature normalized by the superf luid transition temperature is 0.95 at 20 bar, and decreased further t o 0.70 at 0 bar for a thickness of 0.88 mu m for pure He-3. The values of T-AB/T-C were slightly elevated when covering the surface with 4.5 layers of He-4 film, which suggests that this transition is also infl uenced by the surface condition.