Spin Pumping Effect in Superfluid 3He A1

Abstract

A fountain effect is a common phenomenon in both 3He and 4He superfluids. Unique to superfluid 3He is the magnetic fountain effect, which has been used to determine the spin direction of the condensate in 3He A1 phase. Here we present a pressure driven fountain effect in A1 phase. The experimental cell is composed of a large reservoir connected to a small detector chamber through superleak channels of width of 20 μm. One wall of the detector chamber houses a movable circular 6 μm thick membrane which serves as a sensitive capacitive pressure sensor and also acts as a spin pump. In A1 phase, a DC voltage applied on the capacitor induces a simultaneous mass and spin superfluid current into the small chamber. After equilibration, removal of the DC voltage causes a sudden pressure drop followed by a slow relaxation. The sudden drop is a consequence of reversed superfluid flow through the superleak. The observed decay times during the slow relaxation agree with those obtained in magnetically induced spin flow experiment. These observations show that the slow relaxation stems from spin relaxation in the absence of applied field gradient.