Ultrasound investigation of Ce₂Zr₂O₇ at low temperatures and in high magnetic fields.

Through careful controlling the atmosphere during the growth of Ce₂Zr₂O₇ we have been able to stabilize Ce³⁺ and prevent the formation of non-magnetic Ce⁴⁺.¹ This allows us to study the interesting case of doublet-octupole moment on a pyrochlore lattice. In the pyrochlore structure the Ce³⁺ J = 5/2 multiplet is split by crystal field interactions resulting in wave functions for the ground state Kramers doublet which correspond to a linear combination of m_J = ±3/2 states. A generic model for these unusual doublets supports two distinct symmetry enriched U(1) QSL ground states in the corresponding quantum spin ice regimes.² We measured ultrasound down to 20 mK and in magnetic fields of up to 10 T with the field applied along the [111] direction for transversal and longitudinal modes. In zero field we observe a softening of the modes for temperatures below 0.8 K, which is an indication for quantum fluctuations. At 20 mK, an increase of the magnetic field leads to decrease of the sound velocity and the curves show hysteresis which is reminiscent of the behaviour observed in Dy₂Ti₂O₇ and Ho₂Ti₂O₇.

1. H. Otobe et al., J. Phys. Chem. Solids 66, p.329 (2005).
2. Y.D. Li and G. Chen, Phys. Rev. B 95, p.041106(R) (2017).