Dimo I. Uzunov

On the zero temperature critical behaviour of the nonideal Bose gas

Abstract The zero temperature renormalization group recursion relations, their fixed points and the corresponding critical exponents are obtained up to third order in the ϵ-expansion for the nonideal Bose gas in its functional formulation. The considerable simplifications in the zero temperature limit reveal the possibility for an infinite summation of the perturbation series.

Some basic aspects of quantum phase transitions

Several basic problems ofthe theory ofquantum phase transitions are reviewed. The e.ect ofthe quantum correlations on the phase transition properties is considered with the help ofbasic models ofstatistical physics. The e.ect ofquenched disorder on the quantum phase transitions is also discussed. The review is perf ormed within the f ramework ofthe thermodynamic scaling theory and by the most general methods ofstatistical physics for the treatment of phase transitions: general length-scale arguments, exact solutions, mean 3eld approximation, Hubbard–Stratonovich transformation, Feynman path integral approach, and renormalization group in the 3eld theoretical variant. Some new ideas and results are presented. Outstanding theoretical problems are mentioned. c

Correlations, Coherence, and Order

Structural Peculiarities in Fullerene Crystals V.L. Aksenov, V.S. Shakhmatov. Fundamental Problems of Quantum Critical Phenomena L. De Cesare, D.I. Uzunov. Critical Fluctuations in Normal-to-Superconducting Transition R. Folk, Yu. Holovatch. Spin Dynamics of Spin Polarized Fermi Liquids I.A. Fomin. Chaotic Vortices in He II as an Example of Highly Disordered State of One Dimensional Singularities S.K. Nemirovskii. Orientational Disorder and Order in C60-Fullerite and in MC60-Alkali Metal Fullerides A.V. Nikolaev, et al. Desorption Induced by Electronic Transitions: Application to Ionic Compounds M. Piacentini, N. Zema. Strong Electron Correlation Effects in Copper Oxides N.M. Plakida. Quantum Phase Transitions in 2d Quantum Liquids A.M.J. Schakel. List of Contributors. Index.

A mean field study of a very thin ferromagnet

The basis of the mean field theory of small ferromagnetic systems and films is presented through the example of the Ising model. The particular case of a very thin ferromagnet is investigated in detail. New metastable and unstable phases in the very thin ferromagnet are established and described.

Critical behaviour of quantum systems with quenched point impurities

Abstract The effect of quenched point impurities on the critical behaviour of a number of condensed matter systems described by quantum field models is studied by means of the ∈-analysis to order ∈1. The critical dynamic exponent z is calculated. It acquires corrections of order ∈1 for systems with finite critical temperatures (Tc ≠ 0). The quantum (Tc = 0) critical behaviour is unstable with respect to impurity influence.

Critical dynamics of zero-temperature structural phase transitions

The critical dynamics of a class of displacive second-order phase transitions is studied in the limit Tc to 0 (Tc being the critical temperature). Both the renormalisation-group recursion relations method and direct calculation are used for the derivation of the critical exponents up to order epsilon 2 ( epsilon =3-d). The static exponents remain, in some sense, universal, whereas the dynamic exponent has no epsilon corrections.

Phase diagram of a class of spin-triplet ferromagnetic superconductors

Abstract We investigate thermodynamic phases, including the phase of coexistence of superconductivity and ferromagnetism, the possible phase transitions of first and second order, and the shape of the phase diagram in mean-field approximation for a phenomenological model of spin-triplet ferromagnetic superconductors. The results are discussed in view of application to metallic ferromagnets as UGe 2 , ZrZn 2 , URhGe, and Fe.

Random field effects in classical and quantum critical phenomena

The effect of quenched random fields on classical and quantum critical behaviour is studied by means of the ϵ-analysis for a number of systems. The investigation is performed in terms of a generalized random-field correlation function. The interplay of short-range correlations as well as of a parameter-dependent variety of long-range correlations with thermal and quantum fluctuations is revealed.

On the critical slowing down in superconductors

Abstract The critical dynamics in superconductors without magnetic field is studied by straightforward application of the ϵ-expansion technique to a generalized Ginzburg-Landau model. It is shown that the dynamic critical exponent and the time dependent correlation function coincide with those obtained by the TDGL approach.

Fundamental Problems of Quantum Critical Phenomena

The present article is an overview of selected topics rather than a thorough review of the classic and recent achievements in the field of quantum critical phenomena (QCP) — critical phenomena produced by quantum statistical effects in condensed matter and gases. The experimental and theoretical research of QCP is a branch of quantum statistical physics and phase transitions physics of a rapidly growing importance for the explanation of essential features of low dimensional fermion and spin systems, dilute Bose fluids, superconductors, quantum Hall systems, ferroelectrics, etc; as references to recent topics, see, e.g., Sonhdi et al. (1996), Schakel (1997a, 1999), and Caramico D’Auria et al. (1997).