Quantum electric-dipole liquid on a triangular lattice

Abstract

This work was supported by the National Basic Research Program of China (Grant No. 2015CB921201), the National Natural Science Foundation of China (Grant Nos. 11227405, 11534015, 11374347, 11174263 and U1532147) and the Opening Project of Wuhan National High Magnetic Field Center (Grant No. PHMFF2015021). Y.S. also acknowledges the support from Chinese Academy of Sciences (Grants No. XDB07030200 and KJZD-EW-M05).Geometric frustration and quantum fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets. Geometric frustration and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogues of quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19 with geometric frustration represents a promising candidate for the proposed electric-dipole liquid. We present a series of experimental lines of evidence, including dielectric permittivity, heat capacity and thermal conductivity measured down to 66 mK, to reveal the existence of an unusual liquid-like quantum phase in BaFe12O19, characterized by itinerant low-energy excitations with a small gap. The possible quantum liquids of electric dipoles in frustrated dielectrics open up a fresh playground for fundamental physics.Peer reviewe