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The Gibbs canonical distribution, dw~ exp ( - E ( p , q ) / k_B T) dpdq , seems one of the most solid pillars of statistical physics. Thermodynamics is believed to be a derivative of this distribution. Since the temperature Tis introduced, de facto , from a heat bath by the zeroth law of thermodynamics, this distribution cannot represent a genuine temperature fluctuation; all fluctuations are derived from energy fluctuations (E). Increasingly, nanoscale problems are attacked by physics (e.g. glass transition), physical chemistry (e.g. nucleation), or biology (e.g. protein folding). The fluctuations are relatively large because the nano-subsystems are small. The fluctuations should, therefore, completely be collected. The von Laue approach [1 - 3] to subsystem thermodynamics via minimal work for generation of fluctuations also allows the temperature to fluctuate (T). For this alternative, statistical physics is a derivative of thermodynamics. Here we show that a decision between the alternatives is possible by a calorimetric determination of the characteristic length of dynamic glass transition in confined geometries.

The domain structure of the bismuth layered ferroelectric SrBi₂ Ta₂ O₉(SBT) has been studied by group theoretical methods. It is shown that there should exist five types of domain pair independent of one another in SBT, namely: (1) translational domain pairs; (2) 180° (rotational) domain pairs; (3) translational -180° domain pairs; (4) 90° domain pairs; (5) translational -90° domain pairs. In addition, some experimental results are briefly discussed.

The nature of the superionic transition in Ag₂ HgI₄and Cu₂ HgI₄has been investigated using temper dependent powder neutron diffraction and impedance spectroscopy techniques. In the case of Ag₂ HgI₄ , the superionic transition occurs at T_c= 326(2) K and is accompanied by a 50-fold increase in the ionic conductivity. In the Cu⁺analogue, which has a lower conductivity for a given temperature, the corresponding values are T_c= 338(4) K and / ~ 6. The ambient temperature crystal structures of the two compounds are different (space group I for -Ag₂ HgI₄and I 2mfor -Cu₂ HgI₄ ) but, in contrast to the most recent study, the high temperature polymorphs are found to be isostructural (space group F 3m ). Possible explanations for the different behaviour of the ionic conductivity of the two compounds are given.

X-ray absorption spectra of the oxide systems Ba_{1 - x} K_x BiO₃and BaPbO₃above the Bi and Pb L₃absorption edges were investigated. It was shown that oxygen ions move in a double-well potential and their oscillations are correlated with the charge-carrier movement. The observed breathing-like oxygen vibration in the double-well potential with large amplitude and low frequency causes the strong electron-phonon coupling and high T_c -values for doped BaBiO₃ . Based on the experimental data, a model of the relationship of the electronic and local crystal structures is proposed that is in good agreement with the results from transport measurements, and inelastic neutron and electron scattering, Raman scattering, and photoemission spectroscopy. In the framework of the model, the possible reasons for the superconductivity in perovskite-like oxides are discussed.

We consider the effect of interaction on electrons confined to two dimensions at Landau level filling = 2, with the specific aim of determining the range of parameters where the fully polarized state is stable. We calculate the charge- and the spin-density collective modes in the random-phase approximation (RPA) including vertex corrections (also known as the time-dependent Hartree-Fock approximation), and treating the Landau level mixing accurately within the subspace of a single particle-hole pair. It is found that the spin-wave excitation mode of the fully polarized state has a roton minimum which deepens as a result of the interaction-induced Landau level mixing, and the energy of the roton vanishes at a critical Zeeman energy, signalling an instability of the fully polarized state at still lower Zeeman energies. The feasibility of the experimental observation of the roton minimum in the spin-wave mode and its softening will be discussed. The spin- and charge-density collective modes of the unpolarized state are also considered, and a phase diagram for the = 2 state as a function of r_Sand the Zeeman energy is obtained.

A single substitutional impurity in a two-dimensional electron system is studied on the basis of the hybrid Anderson model with s-d coupling only between neighbouring sites. Analytic expressions for local densities of states (DOS) for the impurity d orbitals, d_z²and d_{x²- y²} , and for the s orbitals at the impurity and neighbouring host sites are determined. Special emphasis is put on the appearance of the well-defined resonance states and the antiresonance dips in the spectra, which are discussed in connection with the Fano phenomena. In contrast to the simple s-d Anderson model with the on-site coupling, it is demonstrated that the sharp resonance can be formed by increasing the coupling between the impurity and the host system, and that the resonance energy is shifted towards the band centre where the Van Hove singularity of the host DOS is present.

We report the structural, magnetic and electron transport properties of a new series of compounds where we have substituted Al³⁺in the Mn site of rhombohedral, cation deficient LaMnO₃₊ . All the samples crystallize in rhombohedral (R c ) symmetry with minimal changes in lattice parameters. Mn⁴⁺content gradually decreases from ~25% with increase in Al content and samples with x 15% are stoichiometric without any detectable Mn⁴⁺ . A gradual transition from the ferromagnetic-metallic state to ferromagnetic-insulating state is observed with increase in Al substitution. This indicates a progressive crossover from the double exchange dominated regime indicated by metallicity to the superexchange regime indicated by the absence of Mn⁴⁺across the series. Ferromagnetism in the samples with no Mn⁴⁺is because of ferromagnetic Mn³⁺ -O-Mn³⁺interactions which is possible in the presence of dynamic Jahn-Teller effects in R csymmetry. A semiquantitative estimate of T_Cwas carried out on the basis of near-neighbour exchange interactions and a good agreement with the observed T_Cis reported. Through this the importance of dynamic Jahn-Teller effects coupled with Mn³⁺ -O-Mn³⁺interactions giving rise to ferromagnetism is shown for the whole series. Samples with x 7.5% show a second transition in ac susceptibility at lower temperatures and from the preliminary measurements their origin is attributed to the dynamics of small ferromagnetic clusters arising due to random Al substitution in some of the infinite ferromagnetic matrix.

Using the method of few-body physics, the states of the barrier D^-centre, which consists of a positive ion located on the z -axis at a distance from the two-dimensional quantum dot plane and two electrons in the dot plane bound by the ion, are investigated in a arbitrary strength of magnetic field. This configuration was called a barrier D^-centre. Discontinuous ground-state transitions induced by an external magnetic field have been obtained. The dependence of the binding energy of the ground state of the barrier D^-centre on the dot radius for a few values of the magnetic field strength is obtained.

A zero-field spin-echo nuclear magnetic resonance (NMR) study of ^99,101 Ru nuclei in polycrystalline powder samples of magnetically ordered Sr_{1 - x} Ca_x RuO₃(0x 1.0) is reported. The NMR spectrum for SrRuO₃at 1.3 K consists of two peaks at 64.4 MHz and 72.2 MHz corresponding to the ⁹⁹ Ru and ¹⁰¹ Ru isotopes, respectively, and a hyperfine field of 329 kG. With the replacement of Sr by Ca, the peaks broaden somewhat, although there is essentially no change in the peak frequencies. However, the two resonance peaks show a significant reduction in height with intensity being shifted into the wings. Although electric quadrupole effects are present, the results suggest that the reduction of peak intensity when Ca is added is due mainly to a progressive loss of Ru moments participating in the magnetic ordering. The loss is a consequence of the dilution of the ferromagnetic exchange coupling between the moments. A measure of the spontaneous magnetization temperature dependence for SrRuO₃( 21 K) has been obtained from the shift of the peak frequencies. It was found that the spontaneous magnetization decreases with a Bloch law T^3/2temperature dependence characteristic of spin-wave excitations. From the coefficient of the temperature dependence, a value of 2.4 meV was obtained for the exchange integral which is consistent with the observed ordering temperature.

The dielectric relaxation spectra of NPA (CH₂ OHC(CH₃ )₃ ) and TCE (CH₂ OHCCl₃ ) have been determined in the orientationally disordered state (ODIC) and for TCE also in the liquid state. The studied temperature ranges have been 313-233 K and 293-255 K for NPA and TCE respectively. The frequency dependence of the complex dielectric permittivity is well described in both cases by the Cole-Davidson function. From the fits to this equation, dielectric strengths, relaxation times and spectral shape parameters as functions of temperature have been obtained. The relaxation times are thermally activated following an Arrhenius law for NPA and a Vogel-Fulcher-Tammann law for TCE. Likewise, for NPA a new intermediate ODIC state has been stated by means of dielectric and x-ray diffraction measurements.

The possible existence of a second phase transition in Aurivillius-structure-type ferroelectric compounds is discussed. For this purpose, measurements of the complex elastic (Young's) modulus, dielectric constant, DC conductivity and Raman spectra as a function of temperature have been performed. The results suggest that the anomalies that appear in macroscopic complex elastic modulus, DC conductivity and, probably, those of the 25 cm^-1vibration mode of Raman spectra near the temperature of 300 °C do not correspond to a ferro-paraelectric or ferro-ferroelectric phase transition. Anomalies in the dielectric constant have only been found at the phase transition temperatures. Brillouin measurements show that the 300 °C anomaly is of extrinsic character, which could be connected to shallow point defects caused by the Bi³⁺instability in the Bi₂ O₂layer. With increasing temperature, the defects are ionized increasing the DC conductivity and changing the elastic properties of the material by pinning domain walls or dislocations. Electron spin resonance (ESR) spectra, obtained after heating the samples at T= 500 °C, show the line of the almost free electron from the ionized defects.

Porous semiconductor films (GaAs and GaP) were studied by Fourier-transform infrared reflection spectroscopy, which was shown to enable one to determine their morphologies and such essential parameters for the porous structures as the filling factor.

Photoluminescent, electroluminescent and structural properties of CaS thin films doped with Cu and Ag have been investigated. The emission spectrum and the crystallinity are discussed for different Cu concentrations and different annealing conditions. Codoping with Ag has been evaluated, leading to a more elaborate study of CaS:Cu, Ag layers. The morphology of these layers is investigated with AFM and SEM. Measurements of the PL intensity as a function of working temperature revealed the good quenching behaviour of the layers. For the first time, blue electroluminescent emission could be obtained from a CaS:Cu, Ag thin film system.

The ground-state energies of several interacting electrons confined in a parabolic dot in two dimensions are obtained by using hyperspherical coordinates and high-order perturbation theory. The effect of a perpendicular magnetic field is to change the ground state discontinuously in orbital angular momentum L . The preferred values of Lfor the ground state and the associated electronic structures are studied in detail. It is found that the effective interaction between two electrons moving in different cyclic orbits is a short-range attraction matched to a long-range repulsive tail. Because of this, electrons tend to fill adjacent cyclic orbits and form bunches in the ground states. The effects of an impurity ion are also considered.

There was an error in the energy scale of figure 2, page L251 of this article. The resonant energy has changed from 72.166 meV to 5.209 meV. The lengths d₀ , d₁ , d₂ , d₃and d₄as well as the integers Nand N ´ are unchanged. The correct figure is reproduced below.