Reduced dimensionality in layered quantum dimer magnets: Frustration vs. inhomogeneous condensates

Abstract

Motivated by recent experiments on BaCuSi2O6, we investigate magnetic excitations and quantum phase transitions of layered dimer magnets with inter-layer frustration. We consider two scenarios, (A) a lattice with one dimer per unit cell and perfect inter-layer frustration, and (B) an enlarged unit cell with inequivalent layers, with and without perfect frustration. In all situations, the critical behavior at asymptotically low temperatures is three-dimensional, but the corresponding crossover scale may be tiny. Magnetic ordering in case (B) can be discussed in terms of two condensates; remarkably, perfect frustration renders the proximity effect ineffective. Then, the ordering transition will be generically split, with clear signatures in measurable properties. Using a generalized bond-operator method, we calculate the low-temperature magnetic properties in the paramagnetic and antiferromagnetic phases. Based on the available experimental data on BaCuSi2O6, we propose that scenario (B) with inequivalent layers and imperfect frustration is realized in this material, likely with an additional modulation of the inter-layer couling along the c axis.

23 pages, 18 figs, (v2) new fig for bandwidths, (v3) triplon binding energy discussed, (v4) small changes for clarification, accepted (PRB)

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• Quantum phase transitions
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• Coupled Ladders in a Magnetic Field
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• Dimensional reduction at a quantum critical point
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• Quasiparticle breakdown in a quantum spin liquid
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Cited by in corpus (16)

• Bose-Einstein Condensation in Magnetic Insulators
• Frustration and quantum criticality
• Magnetic frustration in BaCuSi2O6 released
• Emergent Symmetry and Dimensional Reduction at a Quantum Critical Point
• Theory of the field-induced BEC in the frustrated spin-1/2 dimer compound BaCuSi2O6
• Nuclear Magnetic Resonance in High Magnetic Field: Application to Condensed Matter Physics
• Two energy scales of spin dimers in clinoclase Cu3(AsO4)(OH)3
• Spatially Resolved Magnetization in the Bose-Einstein Condensed State of BaCuSi2O6: Evidence for Imperfect Frustration
• Multiple Magnetic Bilayers and Unconventional Criticality without Frustration in BaCuSi${}_2$O${}_6$
• Two types of adjacent dimer layers in the low temperature phase of BaCuSi2O6
• Theory of Magnetic Field-Induced Bose-Einstein Condensation of Triplons in Ba3Cr2O8
• Dimensional crossover in quantum critical metallic magnets
• Bose and Mott Glass Phases in Dimerized Quantum Antiferromagnets
• Magnon Condensation in Dimerized Antiferromagnets with Spin-Orbit Coupling
• Finite-Temperature Transition in the Spin-Dimer Antiferromagnet BaCuSi2O6
• Investigating field-induced magnetic order in Han Purple by neutron scattering up to 25.9 T