Eur. Phys. J. B 55, 429-437 (2007)
https://doi.org/10.1140/epjb/e2007-00065-y

Thermodynamic properties of the XX model in a chain with a period two and three coupling

Departamento de Física Teórica, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain

Corresponding author: ^a julio@unizar.es

Received: 13 January 2006
Revised: 17 July 2006
Published online: 9 March 2007

Abstract

The exact solutions for the energy spectrum of the XX model with a periodic coupling and an external transverse magnetic field h are obtained. The diagonalization procedure is discussed, and analytical and numerical solutions are given. Using the solutions for period-two coupling, the free energy, entropy, and specific heat are calculated as functions of temperature and applied transverse external magnetic field. Their expressions show that below a particular value v and above a value u of the magnetic field |h|, the entropy and the specific heat vanish exponentially in the low temperature limit.