LOW-TEMPERATURE SPECIFIC HEAT STUDY OF SrCu₂(BO₃)₂ WITH AN EXACTLY SOLVABLE GROUND STATE
Kageyama H., Onizuka K., Ueda Y., Nohara M., Suzuki H., Takagi H.

Received: July 22, 1999

PACS: 75.40.-s; 75.40.Cx

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The specific heat of a two-dimensional spin gap system SrCu₂(BO₃)₂ realizing the Shastry-Sutherland model was measured between 1.3 K and 25 K under various magnetic fields up to 12 T. The analysis based on an isolated dimer model in a low temperature region revealed that the value of the spin gap at zero field is Δ=34.4 K. It turned out that Δ decreases in proportion with H due to the Zeeman splitting of the excited triplet levels. This simplest model, however, fails to reproduce the result in a high temperature region, suggesting rather strong spin-spin correlation of the system.