Evidence For First-order Phase Transition Research Articles

Elastic moduli of body-centered cubic lattice near rigidity percolation threshold: Finite-size effects and evidence for first-order phase transition.

Extensive numerical simulations of rigidity percolation with only central forces in large three-dimensional lattices have indicated that many of their topological properties undergo a first-order phase transition at the rigidity percolation threshold p_{ce}. In contrast with such properties, past numerical calculations of the elastic moduli of the same lattices had provided evidence for a second-order phase transition. In this paper we present the results of extensive simulation of rigidity percolation in large body-centered cubic (bcc) lattices, and show that as the linear size L of the lattice increases, the elastic moduli close to p_{ce} decrease in a stepwise, discontinuous manner, a feature that is absent in lattices with L<30. The number and size of such steps increase with L. As p_{ce} is approached, long-range, nondecaying orientational correlations are built up, giving rise to compact, nonfractal clusters. As a result, we find that the backbone of the lattice at p_{ce} is compact with a fractal dimension D_{bb}≈3. The absence of fractal, scale-invariant clusters, the hallmark of second-order phase transitions, together with the stairwise behavior of the elastic moduli, provide strong evidence that, at least in bcc lattices, many of the topological properties of rigidity percolation as well as its elastic moduli may undergo a first-order phase transition at p_{ce}. In relatively small lattices, however, the boundary effects interfere with the nonlocal nature of the rigidity percolation. As a result, only when such effects diminish in large lattices does the true nature of the phase transition emerge.

A new evidence of first-order phase transition for hydrogen at 3000 K

The molecular-dynamics simulations based on density functional theory have been explored to study the properties of warm dense hydrogen in the density range and temperature between 1000 and 3000 K. We find clear evidence of pressure discontinuity at the isotherm of 3000 K by large-scale simulations, which also confirm the first-order nature of this transition. It indicates that the molecular liquid phase is unexpectedly stable, and the temperature of transition towards an atomic liquid phase is much higher than previously predicted. A new transition line has been located in the phase diagram.

From an antiferromagnet to a valence bond solid: evidence for a first-order phasetransition

Using a loop–cluster algorithm we investigate the spin- Heisenberg antiferromagnet on a square lattice with exchange couplingJ and an additional four-spin interaction of strengthQ. We confirm the existence of a phase transition separating antiferromagnetism atJ/Q>Jc/Q from a valence bondsolid (VBS) state at J/Q<Jc/Q. Although our Monte Carlo data are consistent with those of previousstudies, we do not confirm the existence of a deconfined quantumcritical point. Instead, using a flowgram method on lattices as large as802, we find evidence for a weak first-order phase transition. Wealso present a detailed study of the antiferromagnetic phase. ForJ/Q>Jc/Q the staggered magnetization, the spin stiffness and the spinwave velocity of the antiferromagnetare determined by fitting Monte Carlo data to analytic results from the systematic low-energyeffective field theory for magnons. Finally, we also investigate the physics of the VBS state atJ/Q<Jc/Q and we show that long but finite antiferromagnetic correlations are still present.