Weber, LukasFache, Antoine Yves DimitriMila, FredericWessel, Stefan2023-01-302023-01-302023-01-302022-12-1510.1103/PhysRevB.106.235128https://infoscience.epfl.ch/handle/20.500.14299/194427WOS:000901654900003We examine the ground-state phase diagram and thermal phase transitions in a plaquettized fully frustrated bilayer spin-1/2 Heisenberg model. Based on a combined analysis from sign-problem free quantum Monte Carlo simulations, perturbation theory, and free-energy arguments, we identify a first-order quantum phase transition line that separates two competing quantum-disordered ground states with dominant singlet formations on interlayer dimers and plaquettes, respectively. At finite temperatures, this line extends to form a wall of first-order thermal transitions, which terminates in a line of thermal critical points. From a perturbative approach in terms of an effective Ising model description, we identify a quadratic suppression of the critical temperature scale in the strongly plaquettized region. Based on free-energy arguments we furthermore obtain the full phase boundary of the low-temperature dimer-singlet regime, which agrees well with the quantum Monte Carlo data.Materials Science, MultidisciplinaryPhysics, AppliedPhysics, Condensed MatterMaterials SciencePhysicsquantummodeltext::journal::journal article::research article