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Field-induced quantum disordered phases in S=1/2 weakly-coupled dimer systems with site dilution

In the present paper we discuss the rich phase diagram of S=1/2 weakly coupled dimer systems with site dilution as a function of an applied uniform magnetic field. Performing quantum Monte Carlo simulations on a site-diluted bilayer system, we find a sequence of three distinct quantum-disordered phases induced by the field. Such phases divide a doping-induced order-by-disorder phase at low fields from a field-induced ordered phase at intermediate fields. The three quantum disordered phases are: a gapless disordered-free-moment phase, a gapped plateau phase, and two gapless Bose-glass phases. Each of the quantum-disordered phases have distinct experimental signatures that make them observable through magnetometry and neutron scattering measurements. In particular the Bose-glass phase is characterized by an unconventional magnetization curve whose field-dependence is exponential. Making use of a local-gap model, we directly relate this behavior to the statistics of rare events in the system.