TY - JOUR AU - Krasnov, V. O. PY - 2019/01/18 Y2 - 2024/03/28 TI - Fermion Spectrum of Bose–Fermi–Hubbard Model in the Phase with Bose–Einstein Condensate JF - Ukrainian Journal of Physics JA - Ukr. J. Phys. VL - 60 IS - 5 SE - Solid matter DO - 10.15407/ujpe60.05.0443 UR - https://ujp.bitp.kiev.ua/index.php/ujp/article/view/2019236 SP - 443 AB - <p>We investigate the fermion spectrum within the Bose–Fermi–Hubbard model used for the description of boson-fermion mixtures of ultra-cold atoms in optical lattices. We used the method based on the Hubbard operator approach for an on-site basis. The equation for fermion Green’s function in the Bose–Fermi–Hubbard model is built; Green’s functions of higher orders are decoupled in the Hubbard-I approximation (the case of the strong on-site interaction). The corresponding spectral densities are calculated. In the case of hard-core bosons, the condition of appearance of additional bands in the fermion spectrum is investigated. It is shown that these bands exist only in the state with a Bose–Einstein condensate and appear because of the mixing of states with different numbers of bosons. These additional bands can be interpreted as a manifestation of composite excitations (when the appearance of a fermion on the site is accompanied by the simultaneous creation (or annihilation) of a boson).</p> ER -