Quantum electric-dipole liquid on a triangular lattice

TL;DR

This paper proposes the existence of quantum electric-dipole liquids in frustrated dielectric materials, specifically in BaFe12O19, supported by experimental evidence indicating a nontrivial, liquid-like quantum ground state with low-energy excitations.

Contribution

It introduces the concept of quantum electric-dipole liquids in frustrated dielectrics and provides experimental evidence for such a state in BaFe12O19, expanding the scope beyond magnetic systems.

Findings

Evidence of a nontrivial ground state in BaFe12O19

Detection of low-energy excitations with a small gap

Identification of a liquid-like quantum phase

Abstract

Geometric frustrations and quantum mechanical 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 that represents an exotic phase of matter and is attracting enormous interests. Geometric frustrations and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogs to quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled small electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19, in which small electric dipoles originated from the off-center displacement of Fe3+ in the FeO5 bipyramids constitute a two-dimensional triangular lattice, represents a promising candidate to generate the anticipated electric-dipole liquid. We present a series of experimental evidences, including dielectric permittivity, heat capacity, and thermal conductivity measured down to 66 mK, to reveal the existence of a nontrivial ground state in BaFe12O19, characterized by itinerant low-energy excitations with a small gap, to which we interpret as an exotic liquid-like quantum phase. The quantum electric-dipole liquids in frustrated dielectrics open up a fresh playground for fundamental physics and may find applications in quantum information and computation as well.