Neutron Scattering Studies of One-Dimensional Helium

As spatial dimensionality decreases, local stabilizing interactions weaken, leading to the emergence of strongly fluctuating phases of matter without classical analogs, such as spin liquids, Dirac fermions, and the fractional quantum Hall effect in two dimensions (2D). Creating stable one-dimensional (1D) platforms has been particularly challenging, with notable exceptions like spin chains and ultracold low-density gases. A key feature of these systems is their inability to exhibit long-range order, which is essential for their universal description using Tomonaga-Luttinger liquid theory. In previous work, we demonstrated that ⁴He confined within a templated porous material—preplated with a noble gas to enhance dimensional reduction—exhibits one-dimensional behavior. Neutron scattering revealed that the excitations in confined ⁴He are qualitatively distinct from those in two- and three-dimensional superfluid helium, aligning with quantum Monte Carlo calculations. These simulations suggest that three solid layers form, with a one-dimensional liquid located at the center of the pore. Here, we present neutron scattering results as the filling fraction of the one-dimensional core is varied. We observe that the one-dimensional liquid always forms with a fixed density, even as the pore filling increases. The liquid's length grows with increased filling, but its density remains unchanged.