## Variation of the critical order-parameter phase difference with temperature from 0. 4 to 1. 9 K in the flow of superfluid /sup 4/He through a tiny orifice

The temperature dependence of the order-parameter phase difference at the critical rate of flow of superfluid /sup 4/He through a tiny orifice has been studied between 0.4 and 1.9 K. Use was made of a low-frequency two-chamber acoustic resonator at frequencies between 400 and 2900 Hz. The orifice consisted of a hole --170 nm in diameter in a free-standing foil --100 nm thick. The critical phase difference was found in four runs to equal 31 x 2..pi.. rad and in two later runs to equal 16 x 2..pi.. rad at 0.95 K. In all cases the critical phase difference decreasedmore »