Theory of the field-induced BEC in the frustrated spin-1/2 dimer compound BaCuSi2O6

TL;DR

This paper investigates the exotic criticality in the frustrated spin-1/2 dimer compound BaCuSi2O6 under magnetic field, revealing a 2D-like critical exponent and a 3D phase through theoretical and simulation methods.

Contribution

It introduces a frustrated model with two bilayer types and demonstrates how perfect inter-layer frustration affects critical behavior and phase structure.

Findings

Perfect inter-layer frustration yields a 2D-like critical exponent phi=1.

The model predicts a 3D low temperature phase with non-zero triplet populations.

Quantum Monte Carlo reproduces the entire field-temperature phase diagram.

Abstract

Building on recent neutron and NMR experiments, we investigate the field-induced exotic criticality observed in the frustrated spin-1/2 dimer compound BaCuSi2O6 using a frustrated model with two types of bilayers. A semiclassical treatment of the effective hard-core boson model shows that perfect inter-layer frustration leads to a 2D-like critical exponent phi=1 without logarithmic corrections and to a 3D low temperature phase with different but non vanishing triplet populations in both types of bilayers. These results further suggest a simple phenomenology in terms of a field-dependent transverse coupling in the context of which we reproduce the entire field-temperature phase diagram with Quantum Monte Carlo simulations.