On Thursday 23 January, our group member Dario Rossi successfully defended his PhD thesis “Quantum Magnetism in Synthetic Systems“. Dario was jointly supervised by Louk Rademaker and Dima Abanin from Princeton. His work spans two major experimental platforms — moiré materials and quantum simulators — both of which offer fine-grained control over lattice geometry, interaction strengths, and dynamics, opening windows into regimes that conventional condensed-matter experiments cannot reach.
The thesis comprises four projects. The first studies strained multilayers of CrBr₃, where strain spatially modulates the interlayer exchange, alternating between ferromagnetic and antiferromagnetic regions. Dario developed a theoretical framework capturing the resulting non-collinear magnetic textures, demonstrating how moiré engineering alone can stabilize non-trivial magnetic order. The second project examines a WSe₂/WS₂ heterobilayer at three-quarters filling, where electrons form an effective kagome lattice. From a frustrated Heisenberg Hamiltonian derived from the underlying Hubbard model, Schwinger-boson mean-field theory reveals a phase diagram featuring non-collinear orders and, for realistic parameters, a chiral spin liquid — establishing transition-metal dichalcogenide moiré systems as a platform for topological magnetism.
The third and fourth projects turn to superconducting circuit quantum simulators, studying Hamiltonian ramps through a quantum phase transition in the 2D XY model. Correlation lengths scale with ramp rate in a manner broadly consistent with Kibble–Zurek predictions, while a Holstein–Primakoff spin-wave theory developed in the fourth project provides a detailed picture of magnon dynamics, decay, and scattering during the non-equilibrium ramp.
Together, these projects show how frustration, topology, and non-equilibrium dynamics interplay to shape quantum magnetic phenomena in two dimensions.