Quantum Monte Carlo study of the formation of molecular polarizations and the antiferroelectric ordering in squaric acid crystals

TL;DR

This study uses quantum Monte Carlo simulations to explore proton ordering and antiferroelectric phases in squaric acid crystals, revealing a crossover from a liquidlike state to long-range order influenced by geometrical frustration and quantum fluctuations.

Contribution

It introduces a detailed phase diagram for the transverse-field Ising model on a frustrated lattice, highlighting the mechanisms behind polarization formation and ordering in squaric acid.

Findings

Identification of a crossover to a liquidlike paraelectric state with molecular polarizations.

Observation of long-range order emerging from the liquidlike state with enhanced transition temperature.

Detection of a small specific heat anomaly indicating the lifting of degeneracy.

Abstract

Effects of geometrical frustration and quantum fluctuation are theoretically investigated for the proton ordering in a quasi-two-dimensional hydrogen-bonded system, squaric acid crystal. We elucidate the phase diagram for an effective model, the transverse-field Ising model on a frustrated checkerboard lattice, by using quantum Monte Carlo simulation. A crossover to liquidlike paraelectric state with well-developed molecular polarizations is identified, distinguishably from long-range ordering. Emergence of long-range order from the liquidlike state exhibits peculiar aspects originating from the lifting of quasi-macroscopic degeneracy, such as colossal enhancement of the transition temperature and a vanishingly small anomaly in the specific heat.