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 email@example.com
Revised: 17 July 2006
Published online: 9 March 2007
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.
PACS: 05.70.Fh – Phase transitions: general studies / 05.70.Jk – Critical point phenomena / 75.10.Pq – Spin chain models
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2007