Abstract
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 Pr2Ir2O7, 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 Pr2Ir2O7. 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 Pr2Ir2O7. 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.
Highlights
Spin liquids are exotic states with no spontaneous symmetry breaking down to zerotemperature because of the highly entangled and fluctuating spins in frustrated systems
By introducing quantum fluctuations with Jeff = 1/2 moments, quantum spin ice (QSI) states can be stabilized, exhibiting quantum electrodynamics with extra excitations like photons and visons3. (In this paper, we adopt the naming convention that the magnetic monopoles refer to the spin-flip excitation, while the visons refer to the sources of emergent electric fields3.) Yb2Ti2O7, Tb2Ti2O7, and Pr2Zr2O7 are such promising QSI candidates[3]
No long-range magnetic order was observed down to 70 mK evidenced by the magnetic susceptibility measurement, indicating a possible metallic spin liquid ground state, or even a U(1) QSI state[6,13]
Summary
Spin liquids are exotic states with no spontaneous symmetry breaking down to zerotemperature 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 Pr2Ir2O7, which was proposed as a metallic spin liquid located at a zero-field quantum critical point. 5d electrons have drawn much attention in recent years owing to the various quantum phases and transitions therein, which originate from the competition between spin-orbit coupling and electron–electron correlation[4,5] When these two aspects meet in the pyrochlore iridate Pr2Ir2O7, complex phenomena and exotic phases emerge[6,7,8,9,10,11,12,13]. Multiple mechanisms govern the ground state of Pr2Ir2O7, which may induce rich phenomena beyond the spin-ice physics
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