Spin Hamiltonian and Ground State Clues from Neutron Scattering in the Pyrochlore Spin Liquid Candidate, Yb2Ti2O7

Kate Ross (Johns Hopkins University/NCNR)

The nature of the low temperature magnetism in the magnetic pyrochlore Yb2Ti2O7 has been controversial within the geometrical frustration community. Effective S=1/2 quantum spins are associated with Yb in Yb2Ti2O7. These are ferromagnetically-coupled to each other, and possess XY-like symmetry. This should imply that Yb2Ti2O7 possesses a non-frustrated ground state in spite of its underlying pyrochlore lattice. In contrast, many experimental studies have indicated a disordered ground state below a "transition" temperature (Tc~240mK), marked by a specific heat anomaly. Our diffuse neutron scattering above and below Tc show intriguing short range, low dimensional spin correlations, and application of a modest magnetic field at low temperatures induces a quantum phase transition to an ordered, polarized state. We have successfully described the spin waves excitations in the polarized state using a model that relies on a strong anisotropy of nearest neighbor exchange. This model provides an explanation for the geometrically frustrated magnetism in Yb2Ti2O7, which is now revealed to have "quantum spin ice" type interactions. The model also indicates the possibility of a quantum spin liquid ground state.

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