Muon spin rotation study of the rare-earth quantum dimer system Yb₂Si₂O₇

In quantum dimer systems, a zero-field singlet state can give way to Bose-Einstein condensation (BEC) of triplons under applied magnetic field [1]. We will present work on the material Yb₂Si₂O₇, an effective spin-1/2 antiferromagnet where Yb ions form an anisotropic honeycomb lattice with two different bonds length. It is expected that Yb spins form dimers on the shortest Yb-Yb bonds, and the resulting singlet-triplet gap has been observed with specific heat and inelastic neutron scattering. Between critical fields H_C1 = 0.4 T and H_C2 = 1.4 T, an antiferromagnetic phase reminiscent of a BEC of triplons is observed. We will present a low-temperature µSR investigation of this Yb-based quantum dimer system. Below the critical field H_C1, our measurements confirm the lack of magnetic order, yet also exhibit anomalous spin relaxation, which might be explained through hyperfine enhancement or a perturbation of the local environment by the implantation of a muon. At longitudinal magnetic fields near and above H_C1, a dramatic increase in muon spin relaxation, associated with antiferromagnetic order, is observed.

[1] T. Giamarchi, C. Rüegg & O. Tchernyshyov. Nature Physics 4, 198 (2008).