Thermodynamic behavior of Ce compounds tuned at T_ord = 0

TL;DR

This paper classifies Ce compounds based on their magnetic phase diagrams near T_ord=0, revealing different quantum critical behaviors and establishing an upper limit for low-energy excitations consistent with thermodynamics.

Contribution

It provides a detailed classification of Ce compounds' magnetic behaviors near quantum criticality and quantifies the excitation density limit at T=0.

Findings

Ce compounds with S_MO approaching zero as T_ord approaches zero are candidates for quantum criticality.

Phase boundaries ending at finite T Critical Point are due to insufficient decrease in Cm(T_ord) jumps.

Ce heavy fermion systems at T_ord=0 have the highest low-energy excitation density without diverging specific heat.

Abstract

Based on specific heat (C_m) and entropy evaluation, different magnetic phase diagrams of Ce compounds can be recognized: I) with the entropy of the ordered phase (S_MO) decreasing with their order temperature (T_ord): S_MO => 0 as T_ord => 0, being these systems the only candidates for Quantum Critical behavior. II) with phase boundaries ending at a finite temperature Critical Point because their Cm(T_ord) jumps (\Delta C_m) do not decrease sufficiently with T_ord producing a S_MO bottleneck, and III) those showing a transference of degrees of freedom to a non-magnetic heavy fermion (HF) component, with their \Delta C_m vanishing at T >> 0. There is also a IV) group of Ce HF fermions which do not order magnetically because they are tuned at T_ord = 0. These compounds are at the top of the lim(T=>0) of \delta S_m/\delta T = \gamma . values because they collect the highest density of low energy excitations. From the analysis of Cm(T)=T and S_m(T) results performed on these selected Ce ternaries, a quantitative determination of an upper limit for the density of excitations is obtained, excluding any evidence of C_m(T)/T divergency at T => 0 in agreement with thermodynamic laws.