Bi-state Superfluid ³He Weak Links and the Stability of Josephson π States

We have discovered new features of the current-phase relation, I(φ), in superfluid ³He weak links. Firstly, we find that at any given temperature there are two distinct I(φ) functions that characterize the weak link. Secondly, both functions continuously develop an unusual form that ultimately leads to the previously reported π state. The observed form of I(φ) has recently been predicted for unconventional quantum fluids such as ³He, high- T_c superconductors, and Bose-Einstein condensates. The two distinct states are likely to originate from the textural degree of freedom in superfluid ³He.