Thermal conductivity of quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7

Understand

We report low-temperature thermal conductivity $\kappa$ of pyrochlore Yb$_2$Ti$_2$O$_7$, which contains frustrated spin-ice correlations with significant quantum fluctuations.

• In the disordered spin-liquid regime, $\kappa(H)$ exhibits a nonmonotonic magnetic field dependence, which is well explained by the strong spin-phonon scattering and quantum monopole excitations.
• We show that the excitation energy of quantum monopoles is strongly suppressed from that of dispersionless classical monopoles.
• Moreover, in stark contrast to the diffusive classical monopoles, the quantum monopoles have a very long mean free path.