First Principles Study of the Phase Transitions of MnAs

2006 ◽  
Vol 941 ◽  
Author(s):  
Ivan Rungger ◽  
Stefano Sanvito
Keyword(s):  
Phase Transition ◽  
Curie Temperature ◽  
Cell Volume ◽  
Order Phase Transition ◽  
Structural Changes ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
First Order Phase Transition ◽  
The Stability

ABSTRACTThe magnetic and structural properties of MnAs are investigated by mapping ab initio total energies onto a Heisenberg Hamiltonian. We study the dependence of the Curie temperature over the unit cell volume and an orthorhombic distortion by using the mean field approximation, and find that for orthorhombically distorted cells the Curie temperature is much smaller than for hexagonal cells. We provide an explanation for the structural changes of both the first order phase transition at 318 K and the second order phase transition at 400 K, with the cell volume driving the stability of the different structures in the paramagnetic state. The stable cell is found to be orthorhombic up to a critical lattice constant of about 3.7 Å, above which it remains hexagonal.

QCD susceptibilities in the presence of the chiral chemical potential

2020 ◽  
Vol 35 (16) ◽  
pp. 2050137
Author(s):  
Run-Lin Liu ◽  
Hong-Shi Zong
Keyword(s):  
Phase Transition ◽  
Phase Diagram ◽  
Chemical Potential ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Chiral Phase ◽  
First Order Phase Transition ◽  
Phase Transition Region ◽  
First Order Phase

In this paper, chiral chemical potential [Formula: see text] is introduced to investigate the QCD susceptibilities and chiral phase transition within the Polyakov-loop-extended Nambu–Jona-Lasinio models in the mean-field approximation. We concentrate on the effect of chiral chemical potential on the phase diagram and the QCD susceptibilities. Moreover, it is worth noting that chiral chemical potential has more and more prominent impact on the susceptibilities and the phase diagram with the decrease of temperature based on our results, which coincides with the prediction that the chiral symmetry is dynamically broken in the first-order phase transition region and gets partly restored in the crossover region.

Untersuchung des M2/M3-Phasenübergangs in V1-xFexO2 mit x = 0,024.

1976 ◽  
Vol 31 (10) ◽  
pp. 1367-1371 ◽  
Author(s):  
J. Pebler ◽  
K. Schmidt ◽  
H. Wasinski
Keyword(s):  
Phase Transition ◽  
Isomer Shift ◽  
Cell Volume ◽  
Order Phase Transition ◽  
Order Transition ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Transition ◽  
First Order Phase

The Mössbauer investigations of V1-xFexO2 with x = 0.024 indicate that Fe enters two cation positions of M2 and M3. At the phase transition the two quadrupole splittings show a discontinuous behavior whereas the isomer shift changes continuously with a crossingover at the M2, M3 transition (Tt′ = 275 K). Generally a first order phase transition is accompanied by a change of the cell volume V and a change of the isomer shift. The observed continuous behavior of the isomer shift points to a first order transition with δV ≠ 0.

scholarly journals The Smoluchowski Ensemble—Statistical Mechanics of Aggregation

Entropy ◽  
2020 ◽  
Vol 22 (10) ◽  
pp. 1181
Author(s):  
Themis Matsoukas
Keyword(s):  
Sol Gel ◽  
Scaling Limit ◽  
Mean Field ◽  
Central Element ◽  
Field Approximation ◽  
Fixed Number ◽  
Mean Field Approximation ◽  
The Mean ◽  
Sol Gel Transition ◽  
The Stability

We present a rigorous thermodynamic treatment of irreversible binary aggregation. We construct the Smoluchowski ensemble as the set of discrete finite distributions that are reached in fixed number of merging events and define a probability measure on this ensemble, such that the mean distribution in the mean-field approximation is governed by the Smoluchowski equation. In the scaling limit this ensemble gives rise to a set of relationships identical to those of familiar statistical thermodynamics. The central element of the thermodynamic treatment is the selection functional, a functional of feasible distributions that connects the probability of distribution to the details of the aggregation model. We obtain scaling expressions for general kernels and closed-form results for the special case of the constant, sum and product kernel. We study the stability of the most probable distribution, provide criteria for the sol-gel transition and obtain the distribution in the post-gel region by simple thermodynamic arguments.

GROSS–WITTEN POINT AND DECONFINEMENT

2005 ◽  
Vol 20 (19) ◽  
pp. 4469-4474 ◽  
Author(s):  
ROBERT D. PISARSKI
Keyword(s):  
Phase Transition ◽  
Gauge Theory ◽  
Critical Point ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
First Order

Following Aharony et al., we analyze the deconfining phase transition in a SU(∞) gauge theory in mean field approximation. The Gross–Witten model emerges as an "ultra"-critical point for deconfinement: while thermodynamically of first order, masses vanish, asymmetrically, at the transition. Potentials for N = 3 are also shown.

scholarly journals Hybrid Stars in the Framework of NJL Models

2017 ◽  
Vol 45 ◽  
pp. 1760026 ◽  
Author(s):  
Gustavo A. Contrera ◽  
Milva Orsaria ◽  
I. F. Ranea-Sandoval ◽  
Fridolin Weber
Keyword(s):  
Phase Transition ◽  
Quark Matter ◽  
Mean Field ◽  
Field Approximation ◽  
Hadronic Matter ◽  
High Mass ◽  
Mean Field Approximation ◽  
Soft Phase ◽  
Non Local ◽  
Hybrid Stars

We compute models for the equation of state (EoS) of the matter in the cores of hybrid stars. Hadronic matter is treated in the non-linear relativistic mean-field approximation, and quark matter is modeled by three-flavor local and non-local Nambu−Jona-Lasinio (NJL) models with repulsive vector interactions. The transition from hadronic to quark matter is constructed by considering either a soft phase transition (Gibbs construction) or a sharp phase transition (Maxwell construction). We find that high-mass neutron stars with masses up to [Formula: see text] may contain a mixed phase with hadrons and quarks in their cores, if global charge conservation is imposed via the Gibbs conditions. However, if the Maxwell conditions is considered, the appearance of a pure quark matter core either destabilizes the star immediately (commonly for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (generally for local NJL models).

On the stability of two-flavor and three-flavor quark matter in quark stars within the framework of NJL model

2020 ◽  
Vol 35 (39) ◽  
pp. 2050321 ◽  
Author(s):  
Qianyi Wang ◽  
Tong Zhao ◽  
Hongshi Zong
Keyword(s):  
Quark Matter ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Chiral Phase ◽  
Quark Stars ◽  
Njl Model ◽  
The Stability ◽  
Chiral Susceptibility ◽  
Strong Interaction Matter

Following our recently proposed self-consistent mean field approximation approach, we have done some researches on the chiral phase transition of strong interaction matter within the framework of Nambu-Jona-Lasinio (NJL) model. The chiral susceptibility and equation of state (EOS) are computed in this work for both two-flavor and three-flavor quark matter for contrast. The Pauli–Villars scheme, which can preserve gauge invariance, is used in this paper. Moreover, whether the three-flavor quark matter is more stable than the two-flavor quark matter or not in quark stars is discussed in this work. In our model, when the bag constant are the same, the two-flavor quark matter has a higher pressure than the three-flavor quark matter, which is different from what Witten proposed in his pioneering work.

Epitaxial Free Energy and Stability under Epitaxial Strain

1998 ◽  
Vol 05 (05) ◽  
pp. 983-988 ◽  
Author(s):  
P. M. Marcus
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Order Phase Transition ◽  
Tetragonal Phase ◽  
First Order ◽  
Epitaxial Strain ◽  
First Order Phase Transition ◽  
The Stability ◽  
First Order Phase ◽  
Stability Limits

First-principles ground-state total-energy calculations show that tetragonal crystals generally have two structures at which the energy is a minimum, which are appropriately called tetragonal phases in equilibrium. The calculations also show that a small isotropic two-dimensional (epitaxial) strain in the basal plane of a tetragonal phase produces a first-order phase transition to another tetragonal phase, By defining and calculating a special free energy for the states produced by epitaxial strain, the stability limits of each phase and the occurrence of a first-order phase transition between them are clearly demonstrated. Epitaxially strained states and the epitaxial free energy are calculated for vanadium. The epitaxial free energy as a function of the epitaxial stress for these strained states is shown to be similar to free-energy curves calculated for other first-order phase transitions which have analytic descriptions.

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