Elementary Excitations of Bose-Condensed, Spin-Aligned Atomic Hydrogen

Ground-state properties and elementary excitations of superfluid spin-aligned atomic H are studied using methods adapted from the theory of liquid He4. The ground state is a k=0 condensate of the |↓ (electron), ↑ (proton)〉 hyperfine state with a small admixture of |↑↓〉 due to the hyperfine interaction. Excitations can also be labeled approximately by their hyperfine states. ϕ↓↑(k) excitations are phononlike. ϕ↓↑(k) and ϕ↑↓(k) are free-particle-like with energy gaps, and ϕ↑↓(k) excitations resemble spin waves.