ABSTRACT
Two-dimensional magnetism provides a uniquely fertile testing ground for statistical physics, where reduced dimensionality amplifies fluctuations and exposes the mechanisms of collective behaviour. Depending on the dimensionality of the single-ion magnetism, three paradigmatic models structure much of the theoretical landscape: the Ising model, the XY model, and the Heisenberg model. Together, they illustrate how symmetry, dimensionality, and topology govern phase transitions and ordering phenomena in low-dimensional systems, forming the conceptual backbone for modern research on two-dimensional magnetic materials and critical phenomena.
I will talk about our neutron scattering studies of the rare-earth van-der Waals series RE-Br3, which for the most part crystallise in a structure that contains stacked, perfect rare-earth honeycomb lattices. Our single-crystal experiments reveal topological phase transitions and excitations, the presence of quantum fluctuations and the decay of long-lived excitations. I will compare our experimental studies with matrix-product states calculations, where available, which show remarkable agreement. The close quantitative correspondence between these calculations and our experimental results offers fresh insight into the fundamental statistical frameworks that shape our understanding of critical behaviour and dynamical phenomena in low-dimensional systems.
Our results enable us to benchmark microscopic Hamiltonians with unprecedented precision, revealing phenomena that were neither anticipated theoretically nor previously observed experimentally. This combined experimental–theoretical approach not only elucidates the nature of emergent quasiparticles and their interactions, but also establishes a robust framework for investigating universality, confinement, and fractionalisation in two-dimensional quantum magnets.
BIOGRAPHY
Prof. Kenzelmann obtained his D.Phi. in Physics from University of Oxford (Advisor: Prof. Roger Cowley) in 2001, which was followed by post-doctoral fellow at Johns Hopkins University and NIST (Advisor Prof. Collin Broholm). In 2004 he returned to his native Switzerland to become SNF Professor in ETH Zürich & Paul Scherrer Institut (PSI), and has been Head of Laboratory in PSI since 2008. He also holds joint professor appointments in University of Basel and University of Copenhagen.
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