Физика Низких Температур: Том 47, Выпуск 8 (Август 2021), c. 760-773 ( к оглавлению , назад )
Multipole degrees of freedom in physics of high-spin quantum atomic gases
M.S. Bulakhov1,2, A. S. Peletminskii1,2, and Yu. V. Slyusarenko1,2
1Akhiezer Institute for Theoretical Physics, National Science Center “Kharkiv Institute of Physics and Technology” Kharkiv 61108, Ukraine
2V. N. Karazin Kharkiv National University, Kharkiv 61022, Ukraine
Received April 2, 2021, published online June 25, 2021
We provide the general arguments that quantum atomic gases of interacting high-spin atoms represent a physical system in which the multipole (hidden) degrees of freedom may be manifested. Their manifestation occurs when the interatomic interaction is of non-local type. For a local interaction described by the s-wave scattering length, the multipole degrees of freedom do not reveal themselves. To illustrate our findings, we theoretically examine the phenomenon of Bose–Einstein condensation in an interacting gas of spin-1 atoms in an external magnetic field. This study is based on the SU(2) invariant Hamiltonian, which has a bilinear structure in the spin and quadrupole operators along with the scalar term. It is shown that depending on the conditions imposed on the interaction amplitudes (stability conditions), the ground state of the system may exhibit three different phases: quadrupolar, ferromagnetic, and paramagnetic. The basic thermodynamic characteristics affected by hidden degrees of freedom are found for all phases.
Key words: high-spin atoms, quantum atomic gases, Bose–Einstein condensation.