Inhomogeneous superconductivity and the "pseudogap state of novel superconductors

Novel superconducting compounds such as the high Tc oxides are intrinsically inhomogeneous systems. An inhomogeneous structure is created by doping and the statistical nature of the distribution of dopants. Consequently, the critical temperature is spatially dependent: Tc = Tc (r).Comment: 63 pages text, 13 figures and 1 tabl

Surface solitons in quasiperiodic nonlinear photonic lattices

We study discrete surface solitons in semi-infinite, one-dimensional, nonlinear (Kerr), quasiperiodic waveguide arrays of the Fibonacci and Aubry-Andr\'e types, and explore different families of localized surface modes, as a function of optical power content (`nonlinearity') and quasiperiodic strength (`disorder'). We find a strong asymmetry in the power content of the mode as a function of the propagation constant, between the cases of focussing and defocussing nonlinearity, in both models. We also examine the dynamical evolution of a completely-localized initial excitation at the array surface. We find that in general, for a given optical power, a smaller quasiperiodic strength is required to effect localization at the surface than in the bulk. Also, for fixed quasiperiodic strength, a smaller optical power is needed to localize the excitation at the edge than inside the bulk.Comment: 8 pages, 7 figures, submitted for publicatio

Motivational-value factors of success of professional activity of young researchers and teachers

The paper discusses the results of a study of motivational-value sphere of young researchers and teachers. The study revealed the relationship between the characteristics of motivational-value sphere and the success of scientific and educational activities. The article describes the main provisions of the program of non-financial motivation of young researchers and teachers.В статье обсуждаются результаты исследования мотивационно-ценностной сферы молодых научно-педагогических работников. Выявлена взаимосвязь характеристик мотивационно-ценностной сферы и успешности научно-педагогической деятельности. Рассмотрены основные положения программы нематериальной мотивации молодых научно-педагогических работников

An ϵ\epsilon-expansion for Small-World Networks

I construct a well-defined expansion in $\epsilon=2-d$ for diffusion processes on small-world networks. The technique permits one to calculate the average over disorder of moments of the Green's function, and is used to calculate the average Green's function and fluctuations to first non-leading order in $\epsilon$, giving results which agree with numerics. This technique is also applicable to other problems of diffusion in random media.Comment: 7 pages Europhysics style, 3 figure

Two-loop renormalization-group theory for the quasi-one-dimensional Hubbard model at half filling

We derive two-loop renormalization-group equations for the half-filled one-dimensional Hubbard chains coupled by the interchain hopping. Our renormalization-group scheme for the quasi-one-dimensional electron system is a natural extension of that for the purely one-dimensional systems in the sense that transverse-momentum dependences are introduced in the g-ological coupling constants and we regard the transverse momentum as a patch index. We develop symmetry arguments for the particle-hole symmetric half-filled Hubbard model and obtain constraints on the g-ological coupling constants by which resultant renormalization equations are given in a compact form. By solving the renormalization-group equations numerically, we estimate the magnitude of excitation gaps and clarify that the charge gap is suppressed due to the interchain hopping but is always finite even for the relevant interchain hopping. To show the validity of the present analysis, we also apply this to the two-leg ladder system. By utilizing the field-theoretical bosonization and fermionization method, we derive low-energy effective theory and analyze the magnitude of all the excitation gaps in detail. It is shown that the low-energy excitations in the two-leg Hubbard ladder have SO(3) x SO(3) x U(1) symmetry when the interchain hopping exceeds the magnitude of the charge gap.Comment: 18 pages, 9 figures; Two appendices and one figure adde

Temperature dependence of surface magnetization in local-moment systems

We present a theory to study the temperature-dependent behavior of surface states in a ferromagnetic semi-infinite crystal. Our approach is based on the single-site approximation for the \emph{s-f} model. The effect of the semi-infinite nature of the crystal is taken into account by a localized perturbation method. Using the mean-field theory for the layer-dependent magnetization, the local density of states and the electron-spin polarization are investigated at different temperatures for ordinary and surface transition cases. The results show that the surface magnetic properties may differ strongly from those in the bulk and the coupling constant of atoms plays a decisive role in the degree of spin polarization. In particular, for the case in which the exchange coupling constant on the surface and between atoms in the first and second layer is higher than the corresponding in the bulk, an enhancement of surface Curie temperature and hence the spin polarization can be obtained.Comment: 9 pages,8 figure

Survival Probability of a Ballistic Tracer Particle in the Presence of Diffusing Traps

We calculate the survival probability P_S(t) up to time t of a tracer particle moving along a deterministic trajectory in a continuous d-dimensional space in the presence of diffusing but mutually noninteracting traps. In particular, for a tracer particle moving ballistically with a constant velocity c, we obtain an exact expression for P_S(t), valid for all t, for d<2. For d \geq 2, we obtain the leading asymptotic behavior of P_S(t) for large t. In all cases, P_S(t) decays exponentially for large t, P_S(t) \sim \exp(-\theta t). We provide an explicit exact expression for the exponent \theta in dimensions d \leq 2, and for the physically relevant case, d=3, as a function of the system parameters.Comment: RevTeX, 4 page

Spectral and Transport Properties of Quantum Wires with Bond Disorder

Systems with bond disorder are defined through lattice Hamiltonians that are of pure nearest neighbour hopping type, i.e. do not contain on-site contributions. Previous analyses based on the Dorokhov-Mello-Pereyra-Kumar (DMPK) transfer matrix technique have shown that both spectral and transport properties of quasi one-dimensional systems belonging to this category are highly unusual. Notably, regimes with absence of exponential Anderson localization are observed, the single particle density of states exhibits singular structure in the vicinity of the band centre, and the manifestation of these phenomena depends in an apparently topological manner on the even- or oddness of the channel number. In this paper we re-consider the problem from the complementary perspective of the non-linear sigma-model. Relying on the standard analogy between one-dimensional statistical field theories and zero-dimensional quantum mechanics, we will relate the problem to the behaviour of a quantum point particle subject to an Aharonov-Bohm flux. We will re-derive previous DMPK results, identify a new class of even/odd staggering phenomena and trace back the anomalous behaviour of the bond disordered system to a simple physical mechanism, viz. the flux periodicity of the quantum Aharonov-Bohm system. We will also touch upon connections to the low energy physics of other lattice systems, notably disordered chiral systems in 0 and 2 dimensions and antiferromagnetic spin chains.Comment: 55 pages, 2 figures include

Energy relaxation in disordered charge and spin density waves

We investigate collective effects in the strong pinning model of disordered charge and spin density waves (CDWs and SDWs) in connection with heat relaxation experiments. We discuss the classical and quantum limits that contribute to two distinct contribution to the specific heat (a $C_v \sim T^{-2}$ contribution and a $C_v \sim T^{\alpha}$ contribution respectively), with two different types of disorder (strong pinning versus substitutional impurities). From the calculation of the two level system energy splitting distribution in the classical limit we find no slow relaxation in the commensurate case and a broad spectrum of relaxation times in the incommensurate case. In the commensurate case quantum effects restore a non vanishing energy relaxation, and generate stronger disorder effects in incommensurate systems. For substitutional disorder we obtain Friedel oscillations of bound states close to the Fermi energy. With negligible interchain couplings this explains the power-law specific heat $C_v \sim T^{\alpha}$ observed in experiments on CDWs and SDWs combined to the power-law susceptibility $\chi(T)\sim T^{-1+\alpha}$ observed in the CDW o-TaS$_3$.Comment: 13 pages, 10 figures, improvements in the presentatio