We investigate quantum phase transitions in the spin-1/2 Heisenbergantiferromagnet on square lattices with inhomogeneous bond dilution. It isshown that quantum fluctuations can be continuously tuned by inhomogeneous bonddilution, eventually leading to the destruction of long-range magnetic order onthe percolating cluster. Two multicritical points are identified at which themagnetic transition separates from the percolation transition, introducing anovel quantum phase transition. Beyond these multicritical points aquantum-disordered phase appears, characterized by an infinite percolatingcluster with short ranged antiferromagnetic order. In this phase, thelow-temperature uniform susceptibility diverges algebraically withnon-universal exponents. This is a signature that the novel quantum-disorderedphase is a quantum Griffiths phase, as also directly confirmed by thestatistical distribution of local gaps. This study thus presents evidence of agenuine quantum Griffiths phenomenon in a two-dimensional Heisenbergantiferromagnet.
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