arXiv subjects

V. N. Ryzhov

Publications and source records attributed to V. N. Ryzhov.

At least 73 records · Page 4Linked to original sources

arXiv2010

Complex Phase Behavior of The System of Particles with Smooth Potential with Repulsive Shoulder and Attractive Well

We report a detailed simulation study of the phase behavior of core softened system with attractive well. Different repulsive shoulder widthes and attractive well depthes are considered which allows to monitor the influence of repulsive and attractive forces on the phase diagram of the system. Thermodynamic anomalies in the systems are also studied. It is shown that the diffusion anomaly is stabilized by small attraction.

cond-mat.soft↗

arXiv2010

Water-like Anomalies and Breakdown of the Rosenfeld Excess Entropy Scaling Relations for the Core-Softened Systems: Dependence on the Trajectory in Density-Temperature Plane

We show that the existence of the water-like anomalies in kinetic coefficients in the core-softened systems depends on the trajectory in $ρ-T$ plane along which the kinetic coefficients are calculated. In particular, it is shown that the diffusion anomaly does exist along the isotherms, but disappears along the isochores. We analyze the applicability of the Rosenfeld entropy scaling relations to the systems with the core-softened potentials demonstrating the water-like anomalies. It is shown that the validity of the of Rosenfeld scaling relation for the diffusion coefficient also depends on the trajectory in the $ρ-T$ plane along which the kinetic coefficients and the excess entropy are calculated. In particular, it is valid along isochors, but it breaks down along isotherms.

cond-mat.soft↗

arXiv2010

Effective Hamiltonian study of excitations in a boson- fermion mixture with attraction between components

An effective Hamiltonian for the Bose subsystem in the mixture of ultracold atomic clouds of bosons and fermions with mutual attractive interaction is used for investigating collective excitation spectrum. The ground state and mode frequencies of the $^{87}$Rb and $^{40}$K mixture are analyzed quantitatively at zero temperature. We find analytically solutions of the hydrodynamics equations in the Thomas- Fermi approximation. We discuss the relation between the onset of collapse and collective modes softening and the dependence of collective oscillations on scattering length and number of boson atoms.

cond-mat.quant-gas↗

arXiv2010

Transport coefficients of soft sphere fluids at high densities

Molecular dynamics computer simulation has been used to compute the self-diffusion coefficient, and shear viscosity of soft-sphere fluids, in which the particles interact through the soft-sphere or inverse power pair potential. The calculations have been made along the melting line in a wide range of pressures and temperatures. The validity of scaling relations for thermodynamic parameters and kinetic coefficients was checked. It was shown that the Stokes-Einstein relationship is obeyed if the Barker diameter is used as a characteristic length scale. It was also shown that the viscosity is non-monotonic along the isochores as predicted by Ya. Rosenfeld. It was shown that the viscosity is strongly growing along the melting line, however, this increase does not stimulate the glass transition because the relaxation time is decreasing.

cond-mat.soft↗

arXiv2009

Breakdown of The Excess Entropy Scaling for the Systems with Thermodynamic Anomalies

This articles presents a simulation study of the applicability of the Rosenfeld entropy scaling to the systems which can not be approximated by effective hard spheres. Three systems are studied: Herzian spheres, Gauss Core Model and soft repulsive shoulder potential. These systems demonstrate the diffusion anomalies at low temperatures: the diffusion increases with increasing density or pressure. It is shown that for the first two systems which belong to the class of bounded potentials the Rosenfeld scaling formula is valid only in the infinite temperature limit where there are no anomalies. For the soft repulsive shoulder the scaling formula is valid already at sufficiently low temperatures, however, out of the anomaly range.

cond-mat.soft↗

arXiv2008

Waterlike thermodynamic anomalies in a repulsive-step potential system

We report a computer-simulation study of the equilibrium phase diagram of a three-dimensional system of particles with a repulsive step potential. The phase diagram is obtained using free-energy calculations. At low temperatures, we observe a number of distinct crystal phases. We show that at certain values of the potential parameters the system exhibits the water-like thermodynamic anomalies: density anomaly and diffusion anomaly. The anomalies disappear with increasing the repulsive step width: their locations move to the region inside the crystalline phase.

cond-mat.soft↗

arXiv2007

Quasi-binary amorphous phase in a 3D system of particles with repulsive-shoulder interactions

We report a computer-simulation study of the equilibrium phase diagram of a three-dimensional system of particles with a repulsive step potential. Using free-energy calculations, we have determined the equilibrium phase diagram of this system. At low temperatures, we observe a number of distinct crystal phases. However, under certain conditions the system undergoes a glass transition in a regime where the liquid appears thermodynamically stable. We argue that the appearance of this amorphous low-temperature phase can be understood by viewing this one-component system as a pseudo-binary mixture.

cond-mat.soft↗

arXiv2006

Complex Phase Behavior of Repulsive Step Potential Systems in Three Dimensions

The comprehensive computer simulation study of the phase diagram of the repulsive step potential system in three dimensions is represented. We show that the system with a simple purely repulsive isotropic potential demonstrates a number of unusual features. The maxima and minima on the melting curve are found for some regions of potential parameters. It is shown that the phase diagram in $ρ-T$ plane includes two isostructural crystalline parts separated by the disordered phase which is amorphous at low enough temperatures. Phase diagram in the (P-T) plane shows that the transition to the amorphous state occurs approximately along the extrapolated spinodals. Structural FCC-BCC phase transition is found at high densities.

cond-mat.soft↗

arXiv2006

Stable and unstable regimes in Bose-Fermi mixture with attraction between components

A collapse of the trapped boson- fermion mixture with the attraction between bosons and fermions is investigated in the framework of the effective Hamiltonian for the Bose system. The properties of the $^{87}$Rb and $^{40}$K mixture are analyzed quantitatively at $T= 0$. We find numerically solutions of modified Gross- Pitaevskii equation which continuously go from stable to unstable branch. We discuss the relation of the onset of collapse with macroscopic properties of the system. A comparison with the case of a Bose condensate of atomic $^7Li$ system is given.

cond-mat.stat-mech↗

arXiv2005

Generalized van der Waals theory of liquid-liquid phase transitions

In the framework of the thermodynamic perturbation theory for fluids we study how the phase diagram of an isotropic repulsive soft-core attractive potential, where a liquid-liquid phase transition exists in addition to the standard gas-liquid phase transition, changes by varying the parameters of the potential. We show that existence of the liquid-liquid transition is determined by the interplay of the parameters of the potential and the structure of a reference liquid.

cond-mat.stat-mech↗

arXiv2005

Vortex state in Bose-Fermi mixture with attraction between bosons and fermions

Vortex states in the mixture of ultracold atomic clouds of bosons and fermions are investigated using the effective Hamiltonian for the Bose subsystem. A stability of the Bose system in the case of attractive interaction between components is studied in the framework of variational Bose wave function and Thomas-Fermi approximation. It is shown that the critical number of bosons increases in the presence of the vortex.

cond-mat.stat-mech↗

arXiv2004

New Kinds of Phase Transitions: Transformations in disordered Substances

The transitions in disordered substances are discussed briefly: liquid--liquid phase transitions, liquid--glass transition and the transformations of one amorphous form to another amorphous form of the same substances. A description of these transitions in terms of many--particle conditional distribution functions is proposed. The concept of a hidden long range order is proposed, which is connected with the broken symmetry of higher order distribution functions. The appearance of frustration in simple supercooled Lennard--Jones liquid is demonstrated.

cond-mat.dis-nn↗

arXiv2004

Collapse of Bose component in Bose-Fermi mixture with attraction between components

An effective Hamiltonian for the Bose system in the mixture of ultracold atomic clouds of bosons and fermions is obtained by integrating out the Fermi degrees of freedom. An instability of the Bose system is found in the case of attractive interaction between components in good agreement with the experiment on the bosonic $^{87}$Rb and fermionic $^{40}$K mixture.

cond-mat.stat-mech↗

arXiv2004

"Spherical" 3-State Potts Spin Glass: Exact Solution

A continuous 3-state Potts model with an analog of spherical constraints is proposed and is shown to have an exact solution in the case of infinite-ranged interactions. "Spherical" 3-state Potts spin glass model is solved using the known properties of a large random matrix. For this model the results are identical to those obtained by the replica approach for replica symmetric solution.

cond-mat.stat-mech↗

arXiv2003

Low-temperature Phase Transition in 3-state Potts Glass

The low-temperature instability of one-step replica symmetry breaking (1RSB) phase in 3-state Potts spin glass is obtained explicitly. The temperature of the instability is higher than the temperature where the 1RSB entropy becomes negative. The conjecture of the possibility of the low-temperature full RSB is supported.

cond-mat.dis-nn↗

arXiv2003

Cluster model of glass transition in simple liquids

On the basis of microscopic statistical mechanics of simple liquids the orientational interaction between clusters consisting of a particle and its nearest neighbors is estimated. It is shown that there are ranges of density and temperature where the interaction changes sign as a function of a radius of a cluster. The model of interacting cubic and icosahedral clusters is proposed and solved in mean-field replica symmetric approximation. It is shown that the glass order parameter grows smoothly upon cooling, the transition temperature being identified with the temperature of the replica symmetry breaking. It is shown that upon cooling a Lennard-Jones system, cubic clusters freeze first. The transition temperature for icosahedral clusters is about ten per cent lower. So the local structure of Lennard-Jones glass in the vicinity of glass transition should be most probably cubic.

cond-mat.dis-nn↗

arXiv2003

Collapse transition in mixtures of Bosons and Fermions

For mixtures of Bose and Fermi alkali atoms, the Fermion degrees of freedom can be integrated out in their {\bf finite temperature} partition function. The final result can be expanded as a power series in the Boson density. Under appropriate conditions, the pairwise interaction between the bosons can be changed from positive to negative at a low enough temperature by the Fermion-mediated term and the Boson cloud may then collapse. For attractive Fermion-Boson interactions, there is also a collapse of the Fermion cloud. This transition is first order (discontinuous) because the leading order nonlinear interaction term between the Bosons is {\bf third order in Boson density with a negative coefficient}. We discuss the finite temperature phase diagram of this transition. Our result may provide for an explanation of recent experimental observations by Modungo and coworkers.

cond-mat.stat-mech↗

arXiv2002

Reflection symmetry in mean-field replica-symmetric spin glasses

The role of reflection symmetry breaking for the character of the appearance of replica symmetric spin glass state is investigated. We establish the following symmetry rule for classical systems with one order parameter in the replica symmetric mean field approximation. If in the pure system the transition to the ordered phase is of the second order, then in the corresponding random system the glass regime appears as a result of a phase transition; if the transition in the pure system is of the first order, then glass and ordered regimes grow continuously in the random system on cooling.

cond-mat.dis-nn↗