LAUSR

Spin liquids are exotic states with no spontaneous symmetry breaking down to zero-temperature because of the highly entangled and fluctuating spins in frustrated systems. Exotic excitations like magnetic monopoles, visons, and photons may emerge from quantum spin ice states, a special kind of spin liquids in pyrochlore lattices. These materials usually are insulators, with an exception of the pyrochlore iridate Pr 2 Ir 2 O 7 , which was proposed as a metallic spin liquid located at a zero-field quantum critical point. Here we report the ultralow-temperature thermal conductivity measurements on Pr 2 Ir 2 O 7 . The Wiedemann–Franz law is verified at high fields and inferred at zero field, suggesting no breakdown of Landau quasiparticles at the quantum critical point, and the absence of mobile fermionic excitations. This result puts strong constraints on the description of the quantum criticality in Pr 2 Ir 2 O 7 . Unexpectedly, although the specific heats are anisotropic with respect to magnetic field directions, the thermal conductivities display the giant but isotropic response. This indicates that quadrupolar interactions and quantum fluctuations are important, which will help determine the true ground state of this material. Pr 2 Ir 2 O 7 is a candidate for a metallic spin liquid with a quantum critical point; however, the exact nature of its ground state and quantum criticality is unknown. Here, the authors report strong deviations from dipolar spin-ice ground state and find normal electronic behavior near quantum criticality.