Programme

P.49 -- Poster, VCTP-47

Date: Thursday, 4 August 2022

Time: 08:30 - 10:00

Functional integral approach for the Heisenberg model: beyond one-loop approximation

Pham Thi Thanh Nga (1), Nguyen Van Hinh (2) and Nguyen Toan Thang (3)

(1) Electrical and Electronics Engineering, Thuyloi University, 175 Tay Son, Dong Da, Hanoi, Vietnam (2) Department of Fundamental Science, Ha Noi University of Industry, 298 Cau Dien, Bac Tu Liem, Hanoi, Vietnam (3) Institute of Physics, VAST, 10 Dao Tan, Ba Dinh, Hanoi, Vietnam

We study the Heisenberg model by a functional integral method based on the semionic representation of spin operators, suggested by Popov and Fedotov. The partition function of the spin system is written in term of the functional integral over coherent Grassmann variables with an imaginary chemical potential for excluding non-physical states appeared due to the transformation from spin operators to fermionic ones. We go beyond one-loop approximation taking into account coupling between transverse and longitudinal spin components. The magnon energy is derived and compared with one-loop approximation result. The longitudinal excitation appears and is compared with the result obtained by Feynman method.

Presenter: Pham Thi Thanh Nga