Phase transitions in magnetic and superconducting systems with fluctuating valence. Chemical potential evidence

Abstract

We investigate the critical behaviour of the chemical potential and average occupation numbers using the extended s—f model with intersite Cooper pairing for systems with fluctuating valence. The model is able to describe phase transitions from normal ferromagnet to normal paramagnet at Τ = Τc, from superconducting paramagnet to normal paramagnet at Τ = Ts, as well as reentrant phase transitions with three critical temperatures Τs1, Tc and Τs2 (Ts1 < Tc < Τ52). Present investigation, as well as recent results obtained for another models suggest one-to-one correspondence between critical temperatures of the system and kinks appearing in the temperature dependence of the chemical potential and average occupation numbers. This, in turn, indicates a possibility to apply the measurement of the chemical potential vs. temperature as an experimental universal tool when looking for phase transitions in solids.