Theory Group Seminars

Exploring frustration on the triangular lattice: from novel quantum order-by-disorder to BKT physics

by Dr Giacomo Marmorini (Keio University (Tokio, Japan))

Europe/Rome
250

250

Description
Frustrated antiferromagnets are a very rich class of physical systems, in which various new phases of matter are expected to be realized. From a theoretical point of view, however, they present challenging difficulties and typically defy a full quantum treatment, except for specific regions of the parameter space or in one dimension. Employing a combination of analytic and numerical techniques, we determine the ground-state phase diagram of the prototypical spin-1/2 XXZ model on the triangular lattice in a magnetic field and explain the magnetization process of Ba3CoSb2O9. Stimulated by recent evidence of long-range antiferromagnetic order in cold-atom experiments, we explore the thermal phase diagram of the model in the easy-axis region and with transverse field. Away from the highly quantum regime, thermal fluctuations give rise to a nontrivial two-step phase transition through an intermediate phase in which the broken symmetry at zero temperature is partially restored. We discuss how the two transition lines can connect to one of the two Berezinskii–Kosterlitz–Thouless points at zero field.