Temperature dependence of thermopower in underdoped cuprates with strong spin-fermion coupling

Within the spin-fermion model taking into account the real crystalline structure of the CuO 2 plane, the temperature dependence of the normal-state thermopower 𝑆 ⁡ ( 𝑇 ) of cuprate superconductor in the underdoped regime is calculated. The 𝑆 ⁡ ( 𝑇 ) behavior is considered in an ensemble of spin-polaron quasiparticles formed owing to the strong interaction between spins of the oxygen holes and localized copper spins. The kinetic equation is constructed on the basis of the scattering mechanism of the spin polarons on the antiferromagnetic spin fluctuations and solved using the multi-moment method which allows one to exceed the relaxation-time approximation and take into account the scattering anisotropy of carriers properly. Dependence 𝑆 ⁡ ( 𝑇 ) calculated within the five-moment approximation reflects qualitatively the main peculiarities of dependences obtained in experiments on underdoped cuprates. A comparison of obtained results with the results of additional calculations of 𝑆 ⁡ ( 𝑇 ) performed within the 2D Kondo lattice model on a simple square lattice revealed the crucial role of a proper consideration of the spin-fermion coupling on the real CuO 2 plane in describing the temperature behavior of thermopower in underdoped cuprates.