97-21U

# 97-21U

By - Posted on 08 February 2012

UDC:
548:573.611.4
PACS:
75.10.Jm

Thermodynamics of XXZ--model within two-particle cluster approximation

R.R. Levitskii
S.I. Sorokov
O.R. Baran
I.M. Pyndsyn

The XXZ--model was investigated within two--particle cluster approximation with two variational parameters $\varphi^z$, $\varphi^x$. The long--range interaction $J$ was taken into account in the framework of mean--field approximation. At various values of the anisotropy parameter ${\alpha}/{\gamma}$ ($K^{zz}=\gamma K$, $K^{xx}=K^{yy}=\alpha K$, $J^{zz}=\gamma J$, $J^{xx}=J^{yy}=\alpha J$, $K$ -- short--range interaction) and long--range interaction $J$, phase diagrams were constructed and temperature dependences of $\langle S^z \rangle$, $\langle S^x \rangle$, entropy, specific heat, and static susceptibility were calculated. It was shown that at ${\alpha}/{\gamma} \geq 1$ two--particle cluster approximation gave qualitatively incorrect results in a low--temperature region.

Year:
1997
Pages:
31