Bose-Einstein condensation in honeycomb dimer magnets and $\rm Yb_2 \rm Si_2 \rm O_7$

TL;DR

This paper demonstrates a strong match between experimental observations and numerical simulations of Bose-Einstein condensation in a honeycomb lattice quantum magnet, revealing insights into anisotropy effects and phase regimes.

Contribution

It provides a detailed numerical analysis of BEC in a honeycomb dimer magnet, confirming experimental features and elucidating the role of anisotropies and non-linear magnetization behaviors.

Findings

Accurate prediction of critical fields and temperatures of the BEC dome.

Identification of two distinct regimes within the BEC phase.

Confirmation that anisotropies induce a zero-temperature phase transition at low fields.

Abstract

An asymmetric Bose-Einstein condensation (BEC) dome was observed in a recent experiment on the quantum dimer magnet $\rm Yb_2Si_2O_7$, which is modeled by a "breathing" honeycomb lattice Heisenberg model with possible anisotropies. We report a remarkable agreement between key experimental features and predictions from numerical simulations of the magnetic model. Both critical fields, as well as critical temperatures of the BEC dome, can be accurately captured, as well as the occurrence of two regimes inside the BEC phase. Furthermore, we investigate the role of anisotropies in the exchange coupling and the $g$-tensor. While we confirm a previous proposal that anisotropy can induce a zero temperature phase transition at magnetic fields smaller than the fully polarizing field strength, we find that this effect becomes negligible at temperatures above the anisotropy scale. Instead, the two regimes inside the BEC dome are found to be due to a non-linear magnetization behavior of the isotropic breathing honeycomb Heisenberg antiferromagnet. Our analysis is performed by combining the density matrix renormalization group (DMRG) method with the finite-temperature techniques of minimally entangled typical thermal states (METTS) and quantum Monte Carlo (QMC).