August 28th
when: Tuesday 28/08/2018, 13:30
where: KE E-541 (møterom)
speaker: Gøran Nilsen
title: The long road to the kagome lattice antiferromagnet: a few materials met along the way...
abstract:
When geometric frustration - the inability of a magnetic system to satisfy all of its internal interactions - is combined with strong quantum fluctuations, exotic states of matter called spin liquids can result. Beyond being fascinating in their own right, these states have relevance to quantum computing and cryptography, and potentially to high-temperature superconductivity. One of the enduring mysteries in quantum frustrated magnetism is the nature of the spin liquid state in the so-called kagome lattice antiferromagnet, a model which can be described as a two-dimensional tiling of corner-sharing metal-ion triangles. Despite significant recent theoretical progress towards this goal, unequivocal evidence of the predicted states has yet to be observed in experiments. This is partly due to imperfections present in the materials - typically Cu2+-containing minerals - used to study the model. These imperfections include chemical disorder, lattice distortions, and unwanted interactions, all of which conspire to relieve the frustration and generate more conventional magnetic states.
In this talk, I will aim to give an overview of the materials studied as realizations of the kagome lattice antiferromagnet, focusing on two in particular: herbertsmithite (Cu3Zn(OH)6Cl2), and volborthite (Cu3V2O7(OH)2.2H2O). I will aim to show how the crystallography and chemistry of these materials lead to the above imperfections, and discuss their implications in each case. Throughout, the main probe used will be neutron scattering. Although the study of kagome lattice materials shows that realizing the intrinsic features of the model is extremely difficult, it also demonstrates the rich variety of physics which emerges in the presence of quantum fluctuations and geometric frustration.