Thermodynamic properties of an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:mrow></mml:math> ring-exchange model on the triangular lattice
Kazuhiro Seki, Seiji Yunoki
Abstract
By using a numerically exact diagonalization technique and a block-extended version of the finite-temperature Lanczos method, we study thermodynamic properties of an $S=1/2$ Heisenberg model on the triangular lattice with an antiferromagnetic nearest-neighbor interaction $J$ and a four-spin ring-exchange interaction ${J}_{\mathrm{c}}$. Calculations are performed on small clusters under the periodic-boundary conditions. In contrast to the purely triangular case with ${J}_{\mathrm{c}}=0$, the specific heat exhibits a characteristic double-peak structure for ${J}_{\mathrm{c}}/J\ensuremath{\gtrsim}0.04$. From the calculations of the entropy and the uniform magnetic susceptibility, it is shown that nonmagnetic excitations exist below the magnetic excitation for ${J}_{\mathrm{c}}/J\ensuremath{\gtrsim}0.04$.