Search results for "Tricritical point"
showing 6 items of 16 documents
Realization of a two-dimensional Ising system: Deuterium physisorbed on krypton-preplated graphite
2004
Volumetric adsorption isotherm, calorimetric, and neutron diffraction measurements were used to characterize the quantum system ${\mathrm{D}}_{2}$ coadsorbed on graphite preplated by a monolayer of Kr. From the results obtained by these methods a detailed phase diagram of the complete submonolayer coverage range up to the initial stages of bilayer formation could be constructed. The dominant feature of the phase diagram is a commensurate $(1\ifmmode\times\else\texttimes\fi{}1)[\frac{1}{2}]$ structure, which was determined by neutron diffraction. Three phase transitions of this phase were studied: The order-disorder transition at the critical point which, according to the influence of the co…
First Versus Second Order Phase Transitions in the Three-Dimensional Three-State Potts Model in Random Fields
1995
The ordering of three-states Potts ferromagnets on the simple cubic lattice exposed to random fields is investigated by extensive Monte Carlo simulations. Evidence is presented that the transition is second order for intermediate strength of the fields, while it presumably is first order for large field strength. The implications for various theoretical predictions are briefly discussed.
Phase Transitions in Adsorbates with Internal Quantum States
1993
In principle, phase transitions in realistic systems at low temperatures should be studied including quantum effects. However, a full quantum treatment of all degrees of freedom in a simulation is restricted to small systems, if possible at all. In some cases, as is demonstrated for adsorbates, some degrees of freedom can still be modelled classically even at low temperatures, whereas only for the rest a quantum treatment is unavoidable. The path-integral Monte Carlo approach allows a systematic distinction between classical and quantum degrees of freedom in many-body systems. Using this technique in combination with finite-size methods, the complex phase diagram of a two-dimensional model …
Tricritical universality in a two-dimensional spin fluid
1995
Monte Carlo simulations are used to investigate the tricritical point properties of a 2d spin fluid. Measurements of the scaling operator distributions are employed in conjunction with a finite-size scaling analysis to locate the tricritical point and determine the directions of the relevant scaling fields and their associated tricritical exponents. The scaling operator distributions and exponents are shown to match quantitatively those of the 2d Blume-Capel model, confirming that both models belong to the same universality class. Mean-field calculations of the tricritical point properties are also compared with the simulation measurements.
Metals with a Strongly Correlated Electron Liquid
2014
In this chapter, we consider the main properties of strongly correlated Fermi systems, which are formed by the fermion condensate leading to the emergence of flat bands. Namely, we consider the residual entropy \(S_0\) related to the flat bands that leads to the violation of the quasiparticle—hole symmetry. The presence of \(S_0\) has a profound impact on the universality of second order phase transitions. In that case under the application of magnetic field the curve of the second order AF phase transitions passes into a curve of the first order ones at the tricritical point, thus leading to a violation of the critical universality of the fluctuation theory. We demonstrate that a jump in t…
Phase transitions of single polymer chains and of polymer solutions: insights from Monte Carlo simulations
2008
The statistical mechanics of flexible and semiflexible macromolecules is distinct from that of small molecule systems, since the thermodynamic limit can also be approached when the number of (effective) monomers of a single chain (realizable by a polymer solution in the dilute limit) is approaching infinity. One can introduce effective attractive interactions into a simulation model for a single chain such that a swollen coil contracts when the temperature is reduced, until excluded volume interactions are effectively canceled by attractive forces, and the chain conformation becomes almost Gaussian at the theta point. This state corresponds to a tricritical point, as the renormalization gro…