The role of the entropy in the ground state formation of magnetically frustrated systems within their quantum critical regime

Abstract

A systematic modification of the entropy trajectory $S_m(T)$ is observed at very low temperature in magnetically frustrated systems as a consequence of the constraint $S_m\geq 0$ imposed by the third law of thermodynamics. The lack of magnetic order allows to explore some unusual thermodynamic properties by tracing the physical behavior of real systems. The most relevant findings are: i) a common $C_m/T|_{T\to 0} \approx 7$\,J/molK$^2$ 'plateau' in at least five Yb-based very-heavy-fermions VHF compounds; ii) quantitative and qualitative differences between VHF and standard non-Fermi-liquids. iii) Entropy-bottlenecks governing the change of $S_m(T)$ trajectories in a continuous transition into alternative ground states that exhibits third order characteristics. An empirical analysis of the possible $S_m(T\to 0)$ dependencies according to the $\partial ^2 S_m/\partial T^2$ derivative is also preformed. Altogether, this work can be regarded as an empirical application of the third law of thermodynamics.