Diamagnetic phase transition and phase diagrams in beryllium

The model of diamagnetic phase transition in beryllium which takes into account the quasi 2-dimensional shape of the Fermi surface of beryllium is proposed. It explains correctly the recent experimental data on observation of non-homogeneous phase in beryllium at the conditions of strong dHvA effect when the strong correlation of electron gas results in instability of homogeneous phase and formation of Condon domain structure.     

Optical-Phonon Deformation Potentials in Diamond-structure crystals: ab initio LMTO-ASA Calculation

The optical-phonon deformation potentials of C, Si, Ge and Sn are calculated by LMTO-ASA approach within the frozen-phonon approximation. The comparisons between our results and those of several present theoretical calculations and experiments demonstrate that our calculation model is reasonable     

An exact renormalization-group approach for local phonon properties of single-atom and double-atom generalized Fibonacci systems

We present an exact renormalization-group approach to study the local phonon properties of the double-atom generalized Fibonacci systems in which the masses and spring constants are all associated with the aperiodic sequences constructed by the inflation rule: {A, B}{A ⁿ B^m, A}.n(m+1) basic transformations and 2n(n+m–1)+1 basic decimations are introduced. By applying the combinations of derived transformations and decimations, we can determine exactly the renormalized local environment, up to infinite order, of any given site in the double-atom systems. Both the single-atom and double-atom phonon models are employed, and the local density of states in several sites of some generalized Fibonacci systems are numerically calculated.     

Single-particle self-energy and optical conductivity of the simplified Hubbard model

It is shown that the single-particle self-energy of the one and two-dimensional simplified Hubbard model exhibits different behavior characterized by Fermi-liquid, non-Fermi-liquid quasiparticle, or non-quasiparticle excitations, as a function of the strength of the on-site Coulomb repulsionU, temperature, and electron filling. For half-filled lattices, results for the optical conductivity indicate that the d.c. conductivity is zero for all temperatures andU>0.     

Temperature and magnetic field dependencies of Condon domain phase in Lifschitz-Kosevich-Shoenberg approximation

The temperature and magnetic field behavior of non-uniform diamagnetic phase of strongly correlated electron gas at the conditions of the dHvA effect is analyzed. It is shown that in the framework of Lifschitz-Kosevich-Shoenberg approximation the magnetic induction splitting, as well as the range of existence of Condon domains, are characterized by strong dependencies on temperature, magnetic field and impurities of the sample.     

Novel states of electrons on a helium film

Three novel states of electrons on a helium film are described. The first is a diplon, an electron trapped by a positive charge located on a substrate beneath the film, the second is a variation of the first leading to the possibility of a two-dimensional metal-insulator transition, and the third is a ripplonic polaron, an electron self-trapped in a surface dimple. From a survey of experimental searches for the ripplonic polaron state I conclude that no polaron transition occurs on films thicker than 14 nm at T>1.5 K.     

Lanthanum deficiency effect in magnetic transition and transport property of La0.8−δCa0.2MnO3

The evolution of magnetic and electrical phases in La_0.8−δCa_0.2MnO₃ was investigated in terms of La deficiency. We found that the increase of the La deficiency tends to raise the Curie temperature (T_C) in La_0.8−δCa_0.2MnO₃. The FM clusters formed in compounds with large La deficiency provide percolation paths above T_C. With increasing the La defect, the transport property changes from insulating to metallic state, which is in association with the crossover from a second order to a first order magnetic phase transition in the vicinity of T_C.     

Contribution ofd-like states to magnesium,aluminium and phosphorusL-emission bands of MgO,Al2O3 and AlPO4

We have measured the MgL-, AlL- and PL-emission bands of MgO, -Al₂O₃ and AlPO₄, respectively. For MgO and Al₂O₃ the electronic structure and the X-ray emission bands have been calculated. In spite of different crystal structure and chemical composition of these compounds the cationL-emission bands are very similar. We have found that for the interpretation of theL-emission bands of these compounds the cation 3d-like electrons are crucial.     

Reflection properties of metallic photonic crystals

Received: 10 November 1997/Accepted: 16 November 1997     

Occurrence of re-entrant ferromagnetic transitions in rare-earth manganates on cooling the charge-ordered states

Some of the compositions of the half-doped rare-earth manganates, La_0.5−xLn_xCa_0.5MnO₃ (Ln=Nd, Pr) and Nd_0.5Ca_0.5−xSr_xMnO₃ with relatively small A-cation radii, 〈r_A〉, show an unusual behavior wherein they become ferromagnetic (FM) on cooling the charge ordered (CO) state (T_CO>T_C). With increase in 〈r_A〉, however, the T_C becomes greater than T_CO. Thus, plots of T_C and T_CO against 〈r_A〉 for La_0.5−xLn_xCa_0.5MnO₃ (Ln=Nd, Pr) and Nd_0.5Ca_0.5−xSr_xMnO₃ show cross-over from the T_CO>T_C regime to the T_C>T_CO regime around 〈r_A〉 values of 1.195±0.003 and 1.200±0.005 Å, respectively. Between T_C and T_CO, the CO and FM phases are likely to coexist. In Nd_0.5Ca_0.5Mn_1−xM_xO₃ (M=Cr, Ru), T_CO>T_C when x≤0.10, suggesting the re-entrant nature of the FM transition.     

Orbital currents and charge density waves in a generalized Hubbard ladder

We study a generalized Hubbard model on the two-leg ladder at zero temperature, focusing on a parameter region with staggered flux (SF)/d-density wave (DDW) order. To guide our numerical calculations, we first investigate the location of a SF/DDW phase in the phase diagram of the half-filled weakly interacting ladder using a perturbative renormalization group (RG) and bosonization approach. For hole doping δ away from half-filling, finite-system density-matrix renormalization-group (DMRG) calculations are used to study ladders with up to 200 rungs for intermediate-strength interactions. In the doped SF/DDW phase, the staggered rung current and the rung electron density both show periodic spatial oscillations, with characteristic wavelengths 2/δ and 1/δ, respectively, corresponding to ordering wavevectors 2k_F and 4k_F for the currents and densities, where 2k_F = π (1 − δ). The density minima are located at the anti-phase domain walls of the staggered current. For sufficiently large dopings, SF/DDW order is suppressed. The rung density modulation also exists in neighboring phases where currents decay exponentially. We show that most of the DMRG results can be qualitatively understood from weak-coupling RG/bosonization arguments. However, while these arguments seem to suggest a crossover from non-decaying correlations to power-law decay at a length scale of order 1/δ, the DMRG results are consistent with a true long-range order scenario for the currents and densities.     

Anomalous reduction of the β-decay rate due to resonant energy absorption

This paper discusses the temperature dependence of the β-radioactivity rate associated with accompanying energy absorption process in condensed matter. The theoretical estimates are compared with recently reported experimental data.     

Resonant magnetopolaron effects in parabolic quantum wells in a tilted magnetic field

We study the resonant magnetopolaron effects in parabolic quantum wells in a tilted magnetic field. The renormalization of the first excited level, which is resonant with the ground state level plus one longitudinal-optical phonon is calculated at the resonance using an improved resonance approximation to be E= where is the polaron coupling constant. The exponent and the factor are calculated in dependence on the tilt angle of the magnetic field and the confinement energy.     

Extremal entropy for a constrained probability density

The state of extremal entropy for a one-dimensional probability density is considered. This density is constrained by fixed values of the first and second moment. The grandcanonical distribution yields the extremum of the entropy within a certain range of values of the moments. A different type of density corresponds to an extremum of entropy when the moments are outside this range. The shape of this density is approximated with the Ritz variation method. The results are applied to the formation of breathers in the discrete nonlinear Schrödinger equation.     

Exciton dynamics in nanostar dendritic systems using a quantum master equation approach: core monomer effects and possibility of energy transport control

The directional energy transport, i.e. exciton migration, in nanostar dendritic systems composed of two-state monomer units is studied using a quantum master equation approach. We examine the effects of the variation in the excitation energy of the monomer in the core region (core monomer) on the multistep exciton migration from the periphery to the core based on the relaxation factors among exciton states originating in weak exciton-phonon coupling. It turns out that when the core monomer possesses both an excitation energy slightly lower than that of the first generation and a partial exciton overlap with the first generation, more efficient and rapid exciton migration to the core is expected as compared with other core monomer cases with the energy level closer to or much lower than that of the first generation.     

Stable and metastable states and the formation and destruction of breathers in the discrete nonlinear Schrödinger equation

Statistical mechanics explains many localization phenomena of lattices such as the discrete nonlinear Schrödinger equation. However, numerical simulations show that the complete thermalization is rarely achieved. Instead, one observes metastable statistical states that are robust when excited locally. This paper investigates thermodynamically metastable states where the trajectory is confined to some part of the energy shell. The partition function and the entropy are computed with a perturbation method. This method is applicable to stable and metastable states, and it allows us to give approximative analytic expressions for the entropy in the complete thermodynamic state space.     

Relativistic density functional calculation of the total energy and Fermi surface of gold

For fcc gold we have studied the total energy, equilibrium lattice constant, bulk modulus and Fermi surface with their dependence on pressure. The self-consistent calculation in the local-density and warped muffin-tin approximation applies the modified augmented-plane-wave band-method. The core levels are treated in a fully relativistic way and the valence levels in a quasirelativistic approximation on the basis of the Foldy-Wouthuysen transformation. Though the Fermi surface properties and especially the dependence of the extremal orbit areas on pressure are in good agreement with other calculations and experimental values, careful convergence tests offer the quasi-relativistic approximation as source of large errors in the properties which are derived from the total energy.