International Journal of Modern Physics B

The spectroscopical properties of hydrogen (H) and anti-hydrogen atoms in external electric and magnetic fields are discussed. This problem became important in connection with the recent experimental success in production of atoms. The main features of these experiments are briefly reviewed. The proposals for the search of the CPT violation via comparison of the H and spectra are shortly discussed. The spectroscopical differences between H and atoms in external magnetic fields and in parallel magnetic and electric fields are described in detail. It is proven that the positions of the maxima of the frequency distributions for transition probabilities in external electric field for H and atoms will deviate if the non-resonant corrections to the Lorentz line profile are taken into account.

To recognize the distributional characteristics of Fe and Ni doping and the fundamental effects of magnetic ions on superconductivity, the X-ray diffraction, positron annihilation technology and simulated calculations are utilized to investigate systemically YBa₂Cu_3-x(Fe, Ni)_xO_7-δ(x=0.0~0.5). The results show that Fe and Ni doping form different kinds of ion clusters and enter the crystal lattice. When occupying Cu(2) sites in the CuO₂ planes, ions gather into Double Square and/or other clusters, which results in a strong electronic localization and would directly influence the pairing and transportation of carriers, so the superconductivity is suppressed dramatically. While doping ions enter the Cu(1) sites through gathering Hexamer and/or other clusters, this induces the localization of holes and weakens the function of carrier reservoir, so carriers cannot be easily transferred to the CuO₂ planes. However, in this case, the pairing and transportation of carriers are not affected directly, thus the superconductivity is suppressed weakly. Besides, the present results indicate that the superconductivity suppressed has no direct correlation with the magnetism of Fe and Ni ion itself.

Some intermetallic compounds which contain uranium or cerium present heavy fermion characteristics. Take, for example, in the UM₂Al₃ (M=Pd, Ni) family, superconductivity and magnetism coexist and present heavy fermion behavior. This work presents the crystallographic characteristics and physical properties of a new compound of this family; the intermetallic compound UCo₂Al₃. Our initial crystallographic studies performed in a small single crystal show that the structure is hexagonal and similar to the UNi₂Al₃ and UPd₂Al₃ parent compounds. The space group is P6/mmm with a=5.125 Å and c=4.167 Å crystalline parameters. Measurements of resistivity and magnetization performed on the single crystal reveal that the compound is not superconducting when measured at about 1.8 K. The compound is highly anisotropic and features related to Kondo-like behavior are observed. A weak ferromagnetic transition is observed at a temperature of about 20 K.

We find an analytical expression for the conductance of a single electron transistor in the regime when temperature, level spacing and charging energy of a grain are all of the same order. We consider the model of equidistant energy levels in a grain in the sequential tunneling approximation. In the case of spinless electrons, our theory describes transport through a dot in the quantum Hall regime. In the case of spin-½ electrons, we analyze the line shape of a peak, shift in the position of the peak's maximum as a function of temperature and the values of the conductance in the odd and even valleys.

We show that the mechanism of spectral gap formation while switching on periodic perturbation has a "hidden resonance" nature. It consists of a coherent wreck of physical solutions (making them asymptotically unrestricted increasing/decreasing). This notion also gives us paradoxically the key for understanding of wave behavior in allowed zones as alternation of these mutually destructive but compensating regimes resulting in wave beating. The inversion technique also gives rise to zone spectral control algorithms. We reveal a new degree of freedom: the possibility to manipulate the rate of divergence of the solutions in any chosen energy point of the forbidden zone. This forbiddenness makes a deep physical sense, for example, penetration property of separate sectors of heterogeneous structures at chosen energy. We demonstrate examples of application of our theory changing forbiddenness and shifting spectral bands boundaries including instructive merging of zones.

The thermal behaviors of the order-parameters, susceptibility and specific heat of the mixed spin-½ and spin-1 Blume–Capel Ising ferrimagnetic system is studied on the Bethe lattice by using the exact recursion equations. The exact equations for the order parameters and the susceptibility are obtained for the sublattices with spin-1 and spin-½. Also, the exact expressions for the free energy and the specific heat are obtained on the Bethe lattice as a whole system. Then the thermal behaviors of the order-parameters, susceptibility, inverse susceptibility and specific heat are studied for the coordination numbers q=4 and q=6. The obtained results are illustrated and discussed in detail.