Magnetism; Frustration; NMR; muSR; Strong Correlations; Spin Liquid
Majumder Mayukh, Simutis Gediminas, Collings Ines E., Orain Jean-Christophe, Dey Tusharkanti, Li Yuesheng, Gegenwart Philipp, Tsirlin Alexander A. (2020), Persistent spin dynamics in the pressurized spin-liquid candidate YbMgGaO4, in Physical Review Research
, 2(2), 023191-023191.
Magnetic insulators host many physical phenomena from the emblematic field of phase transitions to ordering in complex magnetic structures. In some cases, however, the magnetic order can be destabilized by quantum fluctuations leading to a spin-liquid state with exotic excitations. This has been demonstrated in one dimension but up until recently has remained enigmatic in higher dimensions. Spin liquid state in higher dimensions requires introducing frustration, which prevents a microscopic minimization of interactions between spins. This has long been a realm of theoreticians, but over the last decade some good realizations of frustrated lattices have been discovered and the experimental field is now expanding rapidly. Most notably, the structurally perfect quantum kagome material herbertsmithite (ZnCu3(OH)6Cl2) has been studied extensively. While many physics questions remain, the material issues by now have been mainly solved. This puts us in a perfect position to carry out a dedicated physics research program, studying the effects of perturbation on the ground state and excitations of such systems. Therefore, the objective of the proposed project is to intentionally perturb frustrated magnetic systems and explore the resulting effects which provide information about the unperturbed host system. Such a “perturb too reveal” approach has proven very efficient in other contexts such as one-dimensional antiferromagnetically correlated systems and high temperature superconductors but up until now has been not employed in the context of highly frustrated magnets. The model materials to be studied include the aforementioned herbertsmithite as well as a family of iridate materials where a 3D hyperkagome lattice is realized with emergent phenomena due to strong spin-orbit coupling. The weak Mott insulator in iridate will be pushed into metallic state and the effect on magnetism will be studied. The systems will be perturbed in three ways - substituting with other elements, applying magnetic field and hydrostatic pressure. The effect on the physical properties will be studied using two complementary methods: Nuclear Magnetic Resonance (NMR) and Muon Spin Rotation (muSR) techniques.The project will be carried out in the laboratory of one of the world leaders in the field of frustrated magnetism. The in-house experimental expertise of NMR and muSR techniques will be complemented by the collaborations with theoretical physicists and solid-state chemists. A well-rounded support will enable me to make use of my experience of defects in low-dimensional systems (PhD) and to apply my knowledge of high-pressure muon techniques (post-doc) in order to study the perturbations in frustrated magnets.I will tackle the question of the nature of spin liquids in two and three dimensions. Many problems remain unsolved, including the understanding of the ground state in some model lattices. Additionally, my approach will allow studying impurity-induced effects as well as different quantum phase transitions. A particularly enticing part of the project is to look for the spin textures around the defects, which are bound to show specific features in frustrated magnets. Finally, the study of the iridate hyperkagomes will shed the light on the interplay between charge and spin of the electrons. The proposed project will solidify the understanding of spin liquids and open new avenues of future research.