The effects of disorder in dimerized quantum magnets in mean field approximations

TL;DR

This paper investigates how disorder affects Bose-Einstein condensates of triplon quasiparticles in doped dimerized quantum magnets, revealing parameter renormalization effects and a peak in the Bogoliubov mode speed without evidence of a Bose glass phase.

Contribution

It introduces a mean field approach to model disorder effects in doped quantum magnets and explains magnetization data with disorder-induced parameter renormalization.

Findings

Disorder causes uniform renormalization of system parameters.

The Bogoliubov mode speed peaks as a function of doping.

No evidence of Bose glass phase in the BEC regime.

Abstract

We study theoretically the effects of disorder on Bose-Einstein condensates (BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The condensation occurs in a strong enough magnetic field Hc, where the concentration of bosons in the random potential is sufficient to form the condensate. The effect of doping is partly modeled by delta - correlated disorder potential, which (i) leads to the uniform renormalization of the system parameters and (ii) produces disorder in the system with renormalized parameters. These approaches can explain qualitatively the available magnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In addition to the magnetization, we found that the speed of the Bogoliubov mode has a peak as a function of doping parameter, x. No evidence of the pure Bose glass phase has been obtained in the BEC regime.