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Wednesday, January 25th 2017

1:25 pm:

In a normal magnet strong interactions tend to align the spins in a periodic fashion forming a ferromagnet or an antiferromagnet. However, sometimes when the interactions compete with each other, the spins cannot order into a single low-energy ground state and keep on fluctuating, resulting in highly degenerate ground states with very interesting emergent quantum behavior. Such a ground state is the Kitaev quantum spin liquid (KQSL) which occurs in a honeycomb semiconductor and predicts the emergence of Majorana Fermions and non-abelian anyons that can be used for topological quantum computation. It was proposed that certain d5 materials with a strong octahedral crystal field and a strong spin-orbit coupling in a low-spin ground state can realize a KQSL. In this talk, I will describe the synthesis, ground-state properties and the excitation spectrum of a graphene-like honeycomb magnet a-RuCl3 which complies with the requirements. Using neutron scattering we show that, despite a low-temperature long-range order, the excitation spectrum contains an unusual broad feature matching the predictions of Majorana Fermions arising from strong Kitaev interactions. Detailed theoretical analysis allows us to compare our spectrum with Kitaev exact solutions as well as extensions based on mean-field approximations. Finally, we will talk about our recent endeavors to extend this work using doping, thin-films and application of magnetic field. The later, most interestingly, suppresses the long-range order hopefully leading to a true spin-liquid state.

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