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arXiv · 1201.3532

Continuous and Discontinuous Quantum Phase Transitions in a Model Two-Dimensional Magnet

S. Haravifard·A. Banerjee·J. C. Lang·G. Srajer·D. M. Silevitch·B. D. Gaulin·H. A. Dabkowska·T. F. Rosenbaum
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Abstract

The Shastry-Sutherland model, which consists of a set of spin 1/2 dimers on a 2-dimensional square lattice, is simple and soluble, but captures a central theme of condensed matter physics by sitting precariously on the quantum edge between isolated, gapped excitations and collective, ordered ground states. We compress the model Shastry-Sutherland material, SrCu2(BO3)2, in a diamond anvil cell at cryogenic temperatures to continuously tune the coupling energies and induce changes in state. High-resolution x-ray measurements exploit what emerges as a remarkably strong spin-lattice coupling to both monitor the magnetic behavior and the absence or presence of structural discontinuities. In the low-pressure spin-singlet regime, the onset of magnetism results in an expansion of the lattice with decreasing temperature, which permits a determination of the pressure dependent energy gap and the almost isotropic spin-lattice coupling energies. The singlet-triplet gap energy is suppressed continuously with increasing pressure, vanishing completely by 2 GPa. This continuous quantum phase transition is followed by a structural distortion at higher pressure.

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S. Haravifard, A. Banerjee, J. C. Lang, G. Srajer, D. M. Silevitch, B. D. Gaulin, H. A. Dabkowska, T. F. Rosenbaum. 2012-01-17. Continuous and Discontinuous Quantum Phase Transitions in a Model Two-Dimensional Magnet. https://doi.org/10.1073/pnas.1114464109

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