Entropy-Driven Reentrant Phase Transitions in Even-J/Odd-J Mixtures of Linear Rotors

Freǐman, Yu. A.; Tretyak, S. M.; Mao, Ho‐kwang; Hemley, Russell J.

doi:10.1007/s10909-005-5487-6

Cited by 4 publications

(14 citation statements)

References 8 publications

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“…For the linear rotors the situation is more complicated. As previously found [30] increasing the crystal field causes the appearance of critical points which separate the phase diagram into lines where the phase transition is first order from regions where no phase transition, but a continuous change in the order parameter occurs. An interesting accompanying feature is that where there is a phase transition, the range in which a metastable state is found decreases with the strength of the crystal field.…”

Section: Discussionsupporting

confidence: 56%

“…As has been shown for the three dimensional case [30], the entropy displays an anomaly in the case of the reentrant phase diagram. The entropy curves for the fixed order parameter show qualitatively different behavior above and below T = 0.5, where the slope of the order parameter switches sign (Fig.…”

Section: Coupled Rotors In Two Dimensionssupporting

confidence: 60%

“…When a crystal field is turned on the phase transition is absent for planar rotors, whereas a more complicated situation develops for linear rotors (see Figures 6 and 7 and Ref. [30]), but if the crystal field is large enough the ordering and disordering also happens continuously. The entropy anomaly accompanies all of these ordering patterns.…”

Section: Coupled Rotors In Three Dimensionsmentioning

confidence: 99%

“…Recently a set of studies [29,30,31] have suggested that if the thermal equilibrium distribution of the ortho-para ratio is reached then reentrance can occur in the homonuclear systems H 2 and D 2 . This conclusion is supported by experimental evidence [32].…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

2D and 3D Quantum Rotors in a Crystal Field: Critical Points, Metastability, and Reentrance

Freiman

Hetényi

Tretyak

2010

Metastable Systems Under Pressure

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An overview of results of models of coupled quantum rotors is presented. We focus on rotors with dipolar and quadrupolar potentials in two and three dimensions, potentials which correspond to approximate descriptions of real molecules adsorbed on surfaces and in the solid phase. Particular emphasis is placed on the anomalous reentrant phase transition which occurs in both two and three-dimensional systems. The anomalous behaviour of the entropy, which accompanies the reentrant phase transition, is also analyzed and is shown to be present regardless if a phase transition is present or not. Finally, the effects of the crystal field on the phase diagrams are also investigated. In two-dimensions the crystal field causes the disappearance of the phase transition, and ordering takes place via a continuous increase in the value of the order parameter. This is also true in three dimensions for the dipolar potential. For the quadrupolar potential in three dimensions turning on the crystal field leads to the appearance of critical points where the phase transition ceases, and ordering occurs via

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Section: Discussionsupporting

confidence: 56%

Section: Coupled Rotors In Two Dimensionssupporting

confidence: 60%

Section: Coupled Rotors In Three Dimensionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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2D and 3D Quantum Rotors in a Crystal Field: Critical Points, Metastability, and Reentrance

Freiman

Hetényi

Tretyak

2010

Metastable Systems Under Pressure

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“…Mean-field studies of hydrogen assume that the nuclear spin conversion times are either infinite or instantaneous on rotational time-scales [11]. In this work the intermediate case, where nuclear spin relaxation is long on the timescale of rotation but allowed to equilibrate on the experimental time-scale is investigated.…”

Section: Introductionmentioning

confidence: 99%

Mean-field theory of orientational ordering in rigid rotor models with identical atoms: spin conversion and thermal equilibration

Hetényi

2010

Low Temperature Physics

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In coupled rotor models which describe identical rotating nuclei the nuclear spin states restrict the possible angular momenta of each molecule. There are two mean-field approaches to determining the orientational phase diagrams in such systems. In one the nuclear spin conversion times are assumed to be instantaneous in the other infinite. In this paper the intermediate case, when the spin conversion times are significantly slower than those of rotational time scales, but are not infinite on the time-scale of the experiment, is investigated. Via incorporation of the configurational degeneracy it is shown that in the thermodynamic limit the mean-field approach in the intermediate case is identical to the instantaneous spin conversion time approximation. The total entropy can be split into configurational and rotational terms. The mean-field phase diagram of a model of coupled rotors of three-fold symmetry is also calculated in the two approximations. It is shown that the configurational entropy has a maximum as a function of temperature which shifts to lower temperatures with increasing order.

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Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

Freiman

Crespo

2017

Low Temperature Physics

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The multiple isotopic family of hydrogens (H 2 , HD, D 2 , HT, DT, T 2 ) due to large differences in the de Boer quantum parameter and inertia moments displays a diversity of pronounced quantum isotopic solid-state effects. The homonuclear members of this family (H 2 , D 2 , T 2 ) due to the permutation symmetry are subjects of the constraints of quantum mechanics which link the possible rotational states of these molecules to their total nuclear spin giving rise to the existence of two spin-nuclear modifications, ortho-and parahydrogens, possessing substantially different properties. Consequently, hydrogen solids present an unique opportunity for studying both isotope and spin-nuclear effects. The rotational spectra of heteronuclear hydrogens (HD, HT, DT) are free from limitations imposed by the permutation symmetry. As a result, the ground state of these species in solid state is virtually degenerate. The most dramatic consequence of this fact is an effect similar to the Pomeranchuk effect in 3 He which in the case of the solid heteronuclear hydrogens manifests itself as the reentrant broken symmetry phase transitions. In this review article we discuss thermodynamic and kinetic effects pertaining to different isotopic and spin-nuclear species, as well as problems that still remain to be solved.

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Entropy-Driven Reentrant Phase Transitions in Even-J/Odd-J Mixtures of Linear Rotors

Cited by 4 publications

References 8 publications

2D and 3D Quantum Rotors in a Crystal Field: Critical Points, Metastability, and Reentrance

2D and 3D Quantum Rotors in a Crystal Field: Critical Points, Metastability, and Reentrance

Mean-field theory of orientational ordering in rigid rotor models with identical atoms: spin conversion and thermal equilibration

Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

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