μSR study of the dipole-octupole quantum spin ice candidate Ce2Zr2O7

The ${\mathrm{Ce}}^{3+}$ pseudospin-$1/2$ degrees of freedom in ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ possess both dipolar and octupolar character which enables the possibility of novel quantum spin liquid ground states in this material. Here we report muon spin relaxation and rotation ($\ensuremath{\mu}\mathrm{SR}$) measurements on single-crystal samples of ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ in zero magnetic field and in magnetic fields directed along the $[1,\overline{1},0]$ and $[1,1,1]$ crystallographic directions, and for magnetic fields directed both longitudinal and transverse to the direction of muon polarization. Our zero-field results show no signs of magnetic ordering or spin freezing, consistent with earlier zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements on a powder sample of ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$, and also with the expectations for a quantum spin ice. However, we measure a more gentle relaxation rate for ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ in zero field at low temperatures than was previously reported. This difference in relaxation rate is likely due to the low oxidation and, correspondingly, the high stoichiometry of our single-crystal samples. Longitudinal field measurements confirm that the magnetic dipole moments in ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ remain dynamic at $T=0.1$ K on the microsecond timescale. For both $[1,\overline{1},0]$ and $[1,1,1]$ magnetic fields, our $\ensuremath{\mu}\mathrm{SR}$ Knight shift measurements show a field-induced leveling off of the magnetic susceptibility at low temperature which is qualitatively consistent with corresponding calculations using the numerical-linked-cluster method in combination with recent estimates for the nearest-neighbor exchange parameters of ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$.