Quasi-two-dimensional Bose-Einstein condensation of spin triplets in dimerized quantum magnet Ba$_2$CuSi$_2$O$_6$Cl$_2$

Makiko Okada; Hidekazu Tanaka; Nobuyuki Kurita; Kohei Johmoto; Hidehiro Uekusa; Atsushi Miyake; Masashi Tokunaga; Satoshi Nishimoto; Masaaki Nakamura; Marcelo Jaime; Guillaume Radtke; Andrés Saúl

doi:10.1103/PhysRevB.94.094421

paper

Quasi-two-dimensional Bose-Einstein condensation of spin triplets in dimerized quantum magnet Ba $_{2}$ CuSi $_{2}$ O $_{6}$ Cl $_{2}$

arXiv:1609.00438 · doi:10.1103/PhysRevB.94.094421

Abstract

We synthesized single crystals of composition Ba $_{2}$ CuSi $_{2}$ O $_{6}$ Cl $_{2}$ and investigated its quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi $_{2}$ O $_{6}$ also known as Han purple. Ba $_{2}$ CuSi $_{2}$ O $_{6}$ Cl $_{2}$ has a singlet ground state with an excitation gap of $Δ/ k_{B} = 20.8$ K. The magnetization curves for two different field directions almost perfectly coincide when normalized by the $g$ -factor except for a small jump anomaly for a magnetic field perpendicular to the $c$ axis. The magnetization curve with a nonlinear slope above the critical field is in excellent agreement with exact-diagonalization calculations based on a 2D coupled spin-dimer model. Individual exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate a 2D exchange network and weak frustration between interdimer exchange interactions, supported by weak spin-lattice coupling implied from our magnetostriction data. The magnetic-field-induced spin ordering in Ba $_{2}$ CuSi $_{2}$ O $_{6}$ Cl $_{2}$ is described as the quasi-2D Bose-Einstein condensation of triplets.

9 pages, 7 figures, to appear in Phys. Rev. B

Quasi-two-dimensional Bose-Einstein condensation of spin triplets in dimerized quantum magnet Ba2​CuSi2​O6​Cl2​

Abstract

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Quasi-two-dimensional Bose-Einstein condensation of spin triplets in dimerized quantum magnet Ba $_{2}$ CuSi $_{2}$ O $_{6}$ Cl $_{2}$