High Field Specific Heat of 2D Quantum Spin System SrCu2 (BO3)2

SrCu_{2}(BO_{3})_{2} is a quasi-two-dimensional spin system with a singlet dimer ground state. It is the only known realization of the Shastry-Sutherland model. The unique behavior of this quantum spin liquid results from the interplay between two different fascinating aspects of strongly correlated spin systems: namely geometrical frustration and strong quantum fluctuations.

In this talk, I will present recent measurements of specific heat C(H,T) in continuous magnetic fields $H$ of up to 33 T, and a theory that explains the observed behavior. The model is a Shastry-Sutherland Hamiltonian with additional Dzshaloyinsky-Moriya terms that are crucial to explain some qualitative aspects of the experimental curves. The specific heat is obtained using the finite temperature Lanczos method. Our theoretical analysis of the specific heat and the ESR data as a function of magnetic field strongly indicates the absence of a crystal symmetry which is obtained from crystallography studies. This suggests that the lattice structure is strongly affected by the application of a uniform magnetic field due to an eventual spin-lattice coupling.

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