Specific Heat Anomalies in Solids Described by a Multilevel Model

Autor(es)

de Souza, Mariano ^{[1, 2]} ; Paupitz, Ricardo ^[1] ; Seridonio, Antonio ^{[1, 3]} ; Lagos, Roberto E. ^[1]

Afiliação do(s) autor(es)

^[1] Unesp Univ Estadual Paulista, IGCE, Dept Fis, BR-13506900 Rio Claro, SP - Brazil

^[2] Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz - Austria

^[3] Unesp Univ Estadual Paulista, Dept Quim & Fis, BR-15385000 Ilha Solteira, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Brazilian Journal of Physics; v. 46, n. 2, p. 206-212, APR 2016.
• Citações Web of Science: 2

Resumo

In the field of condensed matter physics, specific heat measurements can be considered as a pivotal experimental technique for characterizing the fundamental excitations involved in a certain phase transition. Indeed, phase transitions involving spin (de Souza et al. Phys. B Condens. Matter 404, 494 (2009) and Manna et al. Phys. Rev. Lett. 104, 016403 (2010)), charge (Pregelj et al. Phys. Rev. B 82, 144438 (2010)), lattice (Jesche et al. Phys. Rev. B 81, 134525 (2010)) (phonons) and orbital degrees of freedom, the interplay between ferromagnetism and superconductivity (Jesche et al. Phys. Rev. B 86, 020501 (2012)), Schottky-like anomalies in doped compounds (Lagos et al. Phys. C Supercond. 309, 170 (1998)), electronic levels in finite correlated systems (Macedo and Lagos J. Magn. Magn. Mater. 226, 105 (2001)), among other features, can be captured by means of high-resolution calorimetry. Furthermore, the entropy change associated with a first-order phase transition, no matter its nature, can be directly obtained upon integrating the specific heat over T, i.e., C(T)IT, in the temperature range of interest. Here, we report on a detailed analysis of the two-peak specific heat anomalies observed in several materials. Employing a simple multilevel model, varying the spacing between the energy levels Delta(i) = (E-i - E-0) and the degeneracy of each energy level g(i), we derive the required conditions for the appearance of such anomalies. Our findings indicate that a ratio of Delta(2)/Delta(1) approximate to 10 between the energy levels and a high degeneracy of one of the energy levels define the two-peaks regime in the specific heat. Our approach accurately matches recent experimental results. Furthermore, using a mean-field approach, we calculate the specific heat of a degenerate Schottky-like system undergoing a ferromagnetic (FM) phase transition. Our results reveal that as the degeneracy is increased the Schottky maximum in the specific heat becomes narrow while the peak associated with the FM transition remains unaffected. (AU)

• Processo FAPESP: 14/15521-9 - Propriedades estruturais e eletrônicas de sistemas moleculares e bidimensionais
• Beneficiário: Ricardo Paupitz Barbosa dos Santos
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 11/22050-4 - Investigação das propriedades termodinâmicas e de transporte de sistemas eletrônicos fortemente correlacionados
• Beneficiário: Valdeci Pereira Mariano de Souza
• Modalidade de apoio: Auxílio à Pesquisa - Regular