Entropy of pair condensed bosons at finite temperatures in optical lattices with bond-charge interaction

Abstract This work contains a quantum rotor analysis of the bond-charge interaction extended Bose–Hubbard model. Adding extended interactions to bosonic optical lattice models reveals new phases of matter to observe and study. Many-body correlations further widen the scope of possible discoveries. The U(1) quantum rotor method used in this work preserves three-body correlations, uncovering the presence of pair condensation in this model. Phase transitions between the normal state and both single and pair bosonic condensation are examined through the lens of the thermal behavior of the two superfluid order parameters and entropy, as well as the impact of bond-charge interaction on the properties of Bose–Einstein condensation in the presence of many-body correlations. At low temperatures and high densities, bond-charge interaction reinforces coherence, improving the critical temperature of Bose–Einstein condensation. It also exhibits a temperature-independent dissipative influence on the system.