Strongly correlated bosons at nonzero temperatures

We investigate the structure of strongly correlated normal Bose liquids and fluids by employing correlated density-matrix (CDM) theory, a generalization of correlated basis functions (CBF) theory to nonzero temperatures. The formalism is applied in a study of structural properties of various correlation functions that characterize the one-body and two-body reduced density matrix elements of a boson system and the associated Fourier transforms such as the static structure function, the exchange structure function, the momentum distribution, and related thermodynamic quantities. We perform a numerical analysis for liquid para-hydrogen, close to the triple point, supercritical 4He gas at temperatures T ≥ 12 K, and fluid and liquid 4He in the normal phase below T = 12 K. The results reveal that H2 and 4He, at T > 12 K, are typical quantum Boltz-mann systems following classical statistics. In contrast, liquid 4He exhibits non-classical effects of particle exchange correlations, when the temperature is lowered toward the Bose-Einstein transition regime. © 2008 World Scientific Publishing Company.