Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4.


The experimental realization of a two dimensional quantum spin liquid has been eagerly sought since first proposed by Anderson in 1973. Recently, Cs2CuCl4, a frustrated 2D quantum antiferromagnet (QAF), has shown potential in this regard triggering immense interest, both experimentally and theoretically. Amongst these studies, different scenarios on the nature of the spin liquid phase were proposed and the presence of exotic magnetic phases in the ground state was noticed. To this date, many of these phases are still obscured and the nature of the spin liquid state remains unsettled. To investigate the above, we present 133Cs Nuclear Magnetic Resonance (NMR)measurements on Cs2CuCl4 at temperature down to 50mK and applied magnetic field up to 15 T. We first demonstrate that Cs NMR is an effective probe of the magnetism in the compound through experiments in the paramagnetic phase. Lower temperature NMR measurements as a function of the strength and orientation of the applied magnetic field provide the most complete picture of the different phases stabilized in Cs2CuCl4. The magnetic character of these phases is discussed in the context of the interplay between quantum fuctuations, frustration and the Dzyaloshinskii-Moriya (DM) interaction. Furthermore, we find evidence of three new phase transitions, as well as an unexpected angular dependence of the saturation field. These findings suggest that the accepted Hamiltonian requires modifications, such as additional DM interactions. In order to probe the nature of the spin liquid state, local magnetization and spin-lattice relaxation rate measurements were performed. A comparison with the result of a variational calculation using Gutzwiller-projected mean-field theory demonstrates the 2D magnetic behavior of the local magnetization. In addition, both temperature and magnetic field dependence of the spin-lattice relaxation rate suggests that the relevant low energy quasiparticle excitations obey fermionic statistics.
Thesis (Ph.D.) -- Brown University (2009)

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Vachon, Marc-Andre, "Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4." (2009). Physics Theses and Dissertations. Brown Digital Repository. Brown University Library.