Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnetBa2CuSi2O6Cl2

Abstract

We synthesized single crystals of composition Ba2CuSi2O6Cl2 and investigated its quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi2O6 also known as Han purple. Ba2CuSi2O6Cl2 has a singlet ground state with an excitation gap of ∆/kB = 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 Ba2CuSi2O6Cl2 is described as the quasi-2D Bose-Einstein condensation of triplets.

Triplon band splitting and topologically protected edge states in the dimerized antiferromagnet

“…This compound crystallizes in an orthorhombic layered structure with each layer composed of antiferromagnetically coupled dimers. The space group was originally reported as Cmce 40 , whereas a slight distortion to Cmc 2 1 is confirmed in the present work, as detailed later, allowing an alternation in the interdimer exchange interactions along the a -axis. Figure 1a illustrates the 2D exchange network in Ba 2 CuSi 2 O 6 Cl 2 .…”

“…Recently, a new two-dimensional (2D) quantum dimer compound Ba 2 CuSi 2 O 6 Cl 2 has been discovered 40 . This compound crystallizes in an orthorhombic layered structure with each layer composed of antiferromagnetically coupled dimers.…”

“…These dimers are coupled via interdimer exchange couplings and with i , j = 1, 2 and α = a, b, forming a 2D exchange network in the ab plane. In fact, the magnetic properties of Ba 2 CuSi 2 O 6 Cl 2 are well characterized by a spin-1/2 quasi-2D dimer system 40 . The magnetization curve is excellently reproduced using the exact diagonalization calculation based on the 2D coupled dimer model, indicative of the strongly two-dimensional characters in the exchange network.…”

“…The magnetization curve is excellently reproduced using the exact diagonalization calculation based on the 2D coupled dimer model, indicative of the strongly two-dimensional characters in the exchange network. Under the assumptions of and ( α = a, b), the exchange constants were estimated as J = 2.42 meV, J p = 0.03 meV, J d = 0.34 meV from the magnetization curve and density functional theory calculations 40 . In addition, the magnetic anisotropy should be very small since magnetic susceptibilities and entire magnetization curves for two different field orientations coincide almost perfectly with each other after being normalized by the g -factors.

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Fiber Bragg Grating Dilatometry in Extreme Magnetic Field and Cryogenic Conditions

“…Sensing of magnetostriction with single mode SiO 2 FBGs in pulsed magnetic fields is successfully utilized at the National High Magnetic Field Laboratory (NHMFL) with a resolution as good as a few parts per hundred million ( ΔL/L ≈ 10 −8 ) in the best cases. This capability allows for the study of a variety of insulating and metallic condensed matter systems including geometrically frustrated magnets, quantum magnets, multiferroics, and uranium- and cerium-based antiferromagnets [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]. Figure 1 shows an example of magnetoelastic effects in pulsed magnetic fields to 60 T at cryogenic temperatures on a sample of uranium dioxide (UO 2 ), which is the most commonly used nuclear fuel.…”