Thermopower Near Magnetic and Order-Disorder Critical Points

Abstract

The thermopower anomalies observed at ferromagnetic, antiferromagnetic, and order-disorder critical points are characterized by specific heat like singularities in the temperature derivatives of the thermopower S. The nature of the anomaly is prescribed by the temperature dependence of the zero time localized spin-spin (or concentration-concentration) correlation functions $g\vec k\left( {t = 0} \right)$ for large momentum transfers ($\left| {\vec k} \right|\sim 2{k_F}$). Inelastic scattering is important as a consequence leading to an expression for the critical thermopower which contains convoluted functions of the frequency dependent localized spin-spin correlation functions $g\overrightarrow k\left(\omega\right)$. The observed temperature dependence of S is thought to reside primarily in the behavior of the resistivity p near the critical temperature, the variation of the thermopower integrals with temperature being rather smooth in this regime. When the momentum transfer is small (e.g. ferromagnetic semiconductors) so that the localized spin system’s fluctuations critically slow down, elastic scattering will dominate the thermopower. In such a case, S is directly proportional to the localized spin-spin correlation function ${g_{2{k_F}}}\left({\omega=0} \right)$.