Фермiонний спектр моделi Бозе–Фермi–Хаббарда у фазi з Бозе-конденсатом

• Дата: 2019
• Автор: Krasnov, V. O.
• Формат: Стаття
• Мова: English
• Опубліковано: Publishing house "Academperiodika" 2019
• Онлайн доступ: https://ujp.bitp.kiev.ua/index.php/ujp/article/view/2019236
• Назва журналу: Ukrainian Journal of Physics

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).