Symmetry breaking of the density distribution of a quantum fluid in a nanoslit.

The phenomenon of symmetry breaking (SB) of the fluid density distribution in a slit between parallel identical solid walls examined previously for a classical fluid (argon) [G. O. Berim and E. Ruckenstein, J. Chem. Phys. 126, 124503 (2007)] is examined for a quantum fluid ((4)He) on the basis of a nonlocal density functional theory. The Lennard-Jones potential was employed for the fluid-fluid and fluid-solid interactions. Regarding the latter interaction potential, it was supposed that each wall generates a hard core repulsion at some distance h(r) from the wall. In addition, the Chizmeshya-Cole-Zaremba (CCZ) potential was considered for the fluid-solid interactions. SB was found at all considered temperatures (0 K < or = T < or = 3.0 K) in ranges of average densities of the fluid which decreased, as for classical fluids, with increasing temperature. It was concluded that the existence of SB does not depend on the value of the parameter h(r), whereas, for classical fluids, SB did not occur when h(r) became smaller than a critical value, h(r,c). For the CCZ potential, the asymmetric (symmetry breaking) density profile can be metastable, whereas for the Lennard-Jones potential when an asymmetric density profile occurred it was always stable (had a smaller free energy than the symmetric profile). No effect of the (4)He transition from nonsuperfluid to superfluid state was detected.