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Abstract: We numerically investigate the phase diagram of two-dimensional site-dilutedcoupled dimer systems in an external magnetic field. We show that this phasediagram is characterized by the presence of an extended Bose glass, notaccessible to mean-field approximation, and stemming from the localization oftwo distinct species of bosonic quasiparticles appearing in the ground state.On the one hand, non-magnetic impurities doped into the dimer-singlet phase ofa weakly coupled dimer system are known to free up local magnetic moments. Thedeviations of these local moments from full polarization along the field can bemapped onto a gas of bosonic quasiparticles, which undergo condensation in zeroand very weak magnetic fields, corresponding to transverse long-rangeantiferromagnetic order. An increasing magnetic field lowers the density ofsuch quasiparticles to a critical value at which a quantum phase transitionoccurs, corresponding to the quasiparticle localization on clusters of localmagnets dimers, trimers, etc. and to the onset of a Bose glass. Strongfinite-size quantum fluctuations hinder further depletion of quasiparticlesfrom such clusters, and thus lead to the appearance of pseudo-plateaus in themagnetization curve of the system. On the other hand, site dilution hinders thefield-induced Bose-Einstein condensation of triplet quasiparticles on theintact dimers, and it introduces instead a Bose glass of triplets. A thoroughnumerical investigation of the phase diagram for a planar system of coupleddimers shows that the two above-mentioned Bose glass phases are continuouslyconnected, and they overlap in a finite region of parameter space, thusfeaturing a two-species Bose glass. The quantum phase transition from Boseglass to magnetic order in two dimensions is marked by novel universalexponents.



Autor: Rong Yu, Omid Nohadani, Stephan Haas, Tommaso Roscilde

Fuente: https://arxiv.org/



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