Excitations in quantum magnets using neutrons and quantum hardware
Prof. Arnab Banerjee
Department of Physics and Astronomy
Purdue University
Quantum magnets at low temperatures offer a fascinating ensemble of new states that could be used not only as future quantum electronic platforms but also as benchmarks for emerging quantum hardware. In the first part of my talk, I will discuss our recent extensive neutron scattering results on Kitaev honeycomb magnet RuCl3 at high field. Spin-1/2 Honeycomb magnet alpha-RuCl3 shows strong bond-directional Kitaev interactions with a low antiferromagnetic ordered moment at zero field. At above 7.3 T in-plane magnetic field, this order is suppressed, revealing a quantum spin liquid state that exhibits a spinon continuum and, arguably, a ½-quantized thermal hall plateau arising from Majorana Fermions by some groups. Here we discuss our recent inelastic neutron data taken between 8 – 14 T to shed light on this enigmatic state. We reveal the evolution of the spinon continuum and its condensation into spinon and magnon bound states at high fields. We further show some recent electrical measurements on metal-RuCl3 devices, which show evidence of characteristic energy scales and transitions relevant to the thermal transport measurements and future spin-liquid-based tunnel junctions.
In the last part of my talk, I will briefly showcase our recent results on the discovery of quantum coarsening on a triangular lattice antiferromagnet - using a quantum annealer. Quantum annealers have more than 1000 interconnected qubits and can now perform quantum quenches within the coherence time of the qubit lattices. We paid careful attention to make sure that all qubits are equal - an essential requirement for magnetic frustration. We show that close to the field-driven critical point of the Kosterlitz-Thouless phase, the dominant quench dynamics are not described by the quantum Kibble-Zurek scaling of the quantum phase transition, but rather a faster coarsening dynamics in an effective two-dimensional XY model in the ordered phase. The implications on actual materials research will be discussed. (arXiv:2403.00091, to appear in Nature Comm.)
Hosted by Prof. Assaf