Quantum Fluctuations Driven Orientational Disordering: A Finite-Size Scaling Study

Abstract

The orientational ordering transition is investigated in the quantum generalization of the anisotropic-planar-rotor model in the low temperature regime. The phase diagram of the model is first analyzed within the mean-field approximation. This predicts at $T=0$ a phase transition from the ordered to the disordered state when the strength of quantum fluctuations, characterized by the rotational constant $\Theta$, exceeds a critical value ${\Theta }_{\mathrm{c}}^{MF}$. As a function of temperature, mean-field theory predicts a range of values of $\Theta$ where the system develops long-range order upon cooling, but enters again into a disordered state at sufficiently low temperatures (reentrance). The model is further studied by means of path integral Monte Carlo simulations in combination with finite-size scaling techniques, concentrating on the region of parameter space where reentrance is predicted to occur. The phase diagram determined from the simulations does not seem to exhibit reentrant behavior; at intermediate temperatures a pronounced increase of short-range order is observed rather than a genuine long-range order.

27 pages, 8 figures, RevTex

References in corpus (1)

• Path Integral Monte Carlo Study of a Model 2D Quantum Paraelectric

Cited by in corpus (3)

• Theoretical evidence for a reentrant phase diagram in {\em ortho-para} mixtures of solid H${}_2$
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• 2D and 3D quantum rotors in a crystal field: critical points, metastability, and reentrance