Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the 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 (1) , Guillaume Radtke , Andres A Saúl (2)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 CINaM - Centre Interdisciplinaire de Nanoscience de Marseille

We synthesized single crystals of composition Ba 2 CuSi 2 O 6 Cl 2 and investigated their 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 /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.

Domaines: Matière Condensée [cond-mat]

Makiko Okada, Hidekazu Tanaka, Nobuyuki Kurita, Kohei Johmoto, Hidehiro Uekusa, et al.. Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnet Ba 2 CuSi 2 O 6 Cl 2. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2016, 94 (9), ⟨10.1103/physrevb.94.094421⟩. ⟨hal-01970678⟩