We study the effects of disorder (quenched randomness) in a two-dimensional square-lattice
S= 1/2 quantum-spin system, the JQ model with a multispin interaction Q supplementing the …

Using quantum Monte Carlo simulations, we study effects of disorder on the S= 1/2
Heisenberg model with exchange constant J on the square lattice supplemented by …

We study the effect of a small density nv of quenched nonmagnetic impurities, ie, vacancy
disorder, in gapped short-range resonating valence bond (RVB) spin liquid states and …

The stochastic series expansion (SSE) quantum Monte Carlo method with directed loops is
very efficient for spin and boson systems. The Heisenberg model and its generalizations …

We find that the first-order quantum phase transitions (QPTs) are characterized by intrinsic
jumps of relevant operators while the continuous ones are not. Based on such an …

The three-dimensional quenched random bond diluted (J 1− J 2) quantum Heisenberg
antiferromagnet is studied on a simple-cubic lattice. Using extensive stochastic series …

We have used the stochastic series expansion quantum Monte Carlo method to study
interacting hard-core bosons on the square lattice with pair-hopping processes …

The Stochastic Series Expansion (SSE) quantum Monte Carlo method with directed loops is
very efficient for spin and boson systems. The Heisenberg model and its generalizations …

The transition between the Néel antiferromagnet and the valence-bond solid state in two
dimensions has become a paradigmatic example of deconfined quantum criticality, a non …

This thesis is a tour-de-force combination of analytic and computational results clarifying and
resolving important questions about the nature of quantum phase transitions in one-and two …