Search results for "Phase Transition"
showing 10 items of 1281 documents
Spherical random-field systems with long-range interactions: general results and application to the Coulomb glass
1993
A classical spherical random-field Hamiltonian with long-range (power-law) interactions is investigated by means of the replica theory. Both ferromagnetic and anti-ferromagnetic interactions are considered. The use of continuous variables instead of Ising variables in the spherical version of the model allows one to calculate the free energy exactly. The existence of an equilibrium phase transition is investigated based on the replica-symmetric solution. The results are applied to the Coulomb-glass model of interacting localized electrons in a disordered solid. This model is shown not to have an equilibrium phase transition for spatial dimensions D 4 the model has a phase transition to an o…
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 …
Geometric phases and criticality in spin systems
2006
A general formalism of the relation between geometric phases produced by circularly evolving interacting spin systems and their criticality behavior is presented. This opens up the way for the use of geometric phases as a tool to study regions of criticality without having to undergo a quantum phase transition. As a concrete example a spin-1/2 chain with XY interactions is presented and the corresponding geometric phases are analyzed. The generalization of these results to the case of an arbitrary spin system provides an explanation for the existence of such a relation.
Phase diagram of the two-channel kondo lattice model in one dimension.
2004
Employing the density matrix renormalization group method and strong-coupling perturbation theory, we study the phase diagram of the $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2)$ Kondo lattice model in one dimension. We show that, at quarter filling, the system can exist in two phases depending on the coupling strength. The weak-coupling phase is dominated by RKKY exchange correlations, while the strong-coupling phase is characterized by strong antiferromagnetic correlations of the channel degree of freedom. These two phases are separated by a quantum critical point. For conduction-band fillings of less than one-quarter, we find a paramagnetic metallic phase at weak coupl…
Theory of first-order phase transitions
1987
An introductory review of various concepts about first-order phase transitions is given. Rules for classification of phase transitions as second or first order are discussed, as well as exceptions to these rules. Attention is drawn to the rounding of first-order transitions due to finite-size or quenched impurities. Computational methods to calculate phase diagrams for simple model Hamiltonians are also described. Particular emphasis is laid on metastable states near first-order phase transitions, on the 'stability limits' of such states (e.g. the 'spinodal curve' of the gas-liquid transition) and on the dynamic mechanisms by which metastable states decay (nucleation and growth of droplets …
Holographic encoding of universality in corner spectra
2017
In numerical simulations of classical and quantum lattice systems, 2d corner transfer matrices (CTMs) and 3d corner tensors (CTs) are a useful tool to compute approximate contractions of infinite-size tensor networks. In this paper we show how the numerical CTMs and CTs can be used, {\it additionally\/}, to extract universal information from their spectra. We provide examples of this for classical and quantum systems, in 1d, 2d and 3d. Our results provide, in particular, practical evidence for a wide variety of models of the correspondence between $d$-dimensional quantum and $(d+1)$-dimensional classical spin systems. We show also how corner properties can be used to pinpoint quantum phase …
The peculiarities of the phase diagram of heavy fermion metal CeCoIn5
2007
We analyze the low temperature experimental magnetic field–temperature H–T phase diagram of CeCoIn5. We demonstrate that its main features can be well explained within Landau quasiparticle picture incorporating the fact that quasiparticles form so-called fermion-condensate (FC) state emerging behind the fermion condensation quantum phase transition (FCQPT). We show that near FCQPT, the fluctuations are strongly suppressed while FC by itself is “protected” from above fluctuations by the first order phase transition. We demonstrate that the electronic system of CeCoIn5 can be shifted from the ordered towards disordered side of FCQPT by the application of magnetic field therefore giving a uniq…
Appearance of Fermion-Condensation Quantum Phase Transition in Fermi Systems
2014
As high-\(T_c\) superconductors are represented primarily by 2D layered structures, in Sect. 5.1 we discuss the superconducting state of a 2D liquid of heavy electrons, and within the framework of Gor’kov microscopic equations construct the Green functions of the FC state. On the other hand, our study can easily be generalized to the 3D case. To show that there is no fundamental difference between the 2D and 3D cases, we derive Green’s functions for the 3D case in Sect. 5.1.1. In Sect. 5.2, we consider the dispersion law and lineshape of single-particle excitations. Section 5.3 is devoted to the behavior of heavy-electron liquid with FC in magnetic field. In Sect. 5.4, we analyze conditions…
Kinetics of Ordered Phases in Finite Spin Systems
1989
We study the growth of the ordered phase in a spin system of finite size suddenly brought below the transition temperature. Such a growth is driven by the instability of the mode corresponding to the largest eigenvalue of the interaction matrix. The relaxation occurs through different regimes according to whether the unstable mode has a negligible or macroscopic amplitude. One regime is characterised by dynamical scaling properties whereas in the other we can distinguish the growth to a macroscopic amplitude followed by rare transitions from one equilibrium amplitude to another. The analysis is carried out in the framework of a dynamical generalisation of the spherical model assuming non-ra…
Thin Ising films with competing walls: A Monte Carlo study.
1995
Ising magnets with a nearest neighbor ferromagnetic exchange interaction J on a simple cubic lattice are studied in a thin film geometry using extensive Monte Carlo simulations. The system has two large L\ifmmode\times\else\texttimes\fi{}L parallel free surfaces, a distance D apart from each other, at which competing surface fields act, i.e., ${\mathit{H}}_{\mathit{D}}$=-${\mathit{H}}_{1}$. In this geometry, the phase transition occurring in the bulk at a temperature ${\mathit{T}}_{\mathit{c}\mathit{b}}$ is suppressed, and instead one observes the gradual formation of an interface between coexisting phases stabilized by the surface fields. While this interface is located in the center of th…