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

TL;DR

This paper studies layered quantum dimer magnets with frustration, revealing how inhomogeneous condensates and layer inequivalence influence magnetic phase transitions and properties, with implications for understanding BaCuSi2O6.

Contribution

It introduces a model considering inequivalent layers and imperfect frustration, showing how these factors affect magnetic ordering and phase transition signatures in layered dimer magnets.

Findings

Critical behavior is three-dimensional at low temperatures.

Perfect frustration suppresses the proximity effect between condensates.

Scenario with inequivalent layers and imperfect frustration likely explains BaCuSi2O6 data.

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.