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arXiv · 1911.04161

Multiple Magnetic Bilayers and Unconventional Criticality without Frustration in BaCuSi$_2$O$_6$

S. Allenspach·A. Biffin·U. Stuhr·G. S. Tucker·S. Ohira-Kawamura·M. Kofu·D. J. Voneshen·M. Boehm·B. Normand·N. Laflorencie·F. Mila·Ch. Rüegg
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Abstract

The dimerized quantum magnet BaCuSi$_2$O$_6$ was proposed as an example of "dimensional reduction" arising near the magnetic-field-induced quantum critical point (QCP) due to perfect geometrical frustration of its inter-bilayer interactions. We demonstrate by high-resolution neutron spectroscopy experiments that the effective intra-bilayer interactions are ferromagnetic, thereby excluding frustration. We explain the apparent dimensional reduction by establishing the presence of three magnetically inequivalent bilayers, with ratios 3:2:1, whose differing interaction parameters create an extra field-temperature scaling regime near the QCP with a non-trivial but non-universal exponent. We demonstrate by detailed quantum Monte Carlo simulations that the magnetic interaction parameters we deduce can account for all the measured properties of BaCuSi$_2$O$_6$, opening the way to a quantitative understanding of non-universal scaling in any modulated layered system.

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S. Allenspach, A. Biffin, U. Stuhr, G. S. Tucker, S. Ohira-Kawamura, M. Kofu, D. J. Voneshen, M. Boehm, B. Normand, N. Laflorencie, F. Mila, Ch. Rüegg. 2020-05-06. Multiple Magnetic Bilayers and Unconventional Criticality without Frustration in BaCuSi$_2$O$_6$. https://doi.org/10.1103/physrevlett.124.177205

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