Interpretation of heat capacity anomalies: low temperature antiferromagnetism in

¹ CEA, DRFMC/SPSMS - Av. des Martyrs, Grenoble, France
² ILL - 6 rue Jules Horawitz, 38042 Grenoble, France

Received: 22 January 2004
Accepted: 16 April 2004

Abstract

Since the early experiments on critical opalescence, heat capacity anomalies, which herald continuous transitions of phase, are frequently given microscopic interpretation through an appropriate space-time correlation function. Unfortunately, the global nature of the probe often results in an ill-defined spectral representation of the integrated modes and, as such, help is often sought in the general theoretical consensus of the temporal slowing down and spatial divergence of the critical modes. In this letter it is explicitly shown how a large and continuous anomaly in the heat capacity, which announces the antiferromagnetic phase transition in as established by independent neutron diffraction techniques, is not associated with a critical slowing down of spatially correlated modes but, surprisingly, with a stiffening of spatially local excitations. It appears that the results may be of relevance in the study of other strongly correlated electron systems.