We predict an inhomogeneous phase of superfluid 3He films in which translational symmetry is spontaneously broken in the plane of the film. This phase is energetically favored over a range of film thicknesses, $D_{ c_2}(T)<D<D_{ c_1}(T)$, separating distinct homogeneous superfluid phases. The instability at the critical film thickness, $D_{ c_2}\approx 9 \xi(T)$, is a single-mode instability generating striped phase order in the film. Numerical calculations of the order parameter and free energy indicate a second-order instability to a periodic lattice of degenerate B-like phases separated by domain walls at $D_{ c_1}\approx 12 \xi(T)$. The striped phase should be identifiable in transport and nuclear magnetic resonance experiments.
Categories: cond-mat.supr-con