High Temperature Expansion for the SU(n) Heisenberg Model in One Dimension

Thermodynamic properties of the SU($n$) Heisenberg model in one dimension is studied by means of high-temperature expansion for arbitrary $n$. The specific heat up to $O[(\beta J)^{23}]$ and the correlation function up to $O[(\beta J)^{18}]$ are derived with $\beta J$ being the antiferromagnetic exchange in units of temperature. It is found for $n>2$ that the specific heat shows a shoulder in the high-temperature side of a peak. The origin of this structure is clarified by deriving the temperature dependence of the correlation function. With decreasing temperature, the short-range correlation with two-site periodicity develops first, and then another correlation with $n$-site periodicity at lower temperature. This behavior is in contrast to that of the inverse square interaction model, where the specific heat shows a single peak according to the exact solution. Our algorithm has an advantage that neither computational time nor memory depends on the multiplicity $n$ per site; the series coefficients are obtained as explicit functions of $n$.