International Journal of Modern Physics B

We have analyzed here the recent development towards our understanding of the Integral and Fractional Quantum Hall effect. It has been pointed out that the chiral anomaly and Berry phase approach embraces in a unified way the whole spectrum of quantum Hall systems with their various characteristic features. This formalism also helps us to understand the edge states observed in Hall fluids. It is argued that Hall fluids with even denominator filling factor leads to the non-Abelian Berry phase.

The spin-one-half Falicov–Kimball model for electronically driven valence and metal–insulator transitions is studied in one and two dimensions using small-cluster exact-diagonalization calculations. Performing an exhaustive study of the model close to the metal–insulator transition we have found that the spin-one-half Falicov–Kimball model can describe much of experimental data of transition-metal and rare-earth compounds. Particularly, except the discontinuous transitions it can provide the qualitative explanation for all typical behaviors of the electrical conductivity observed experimentally in these materials.

We study a two-dimensional superconductor in close proximity to a two-dimensional metallic sheet. The electrons in the superconducting sheet are coupled to those in the metallic sheet by the Coulomb interaction only. We obtain an effective phase-only action for the superconductor by integrating out all the electronic degrees of freedom in the problem. The Coulomb drag of the normal electrons in the metallic sheet is found to make the spectrum of phase-fluctuations in the superconductor, dissipative at long wavelengths. The dissipative co-efficient η is shown to be simply related to the normal state conductivities of the superconducting layer (σ_S) and the metallic sheet (σ_E) by the relation η∝σ_Sσ_E/(σ_S+σ_E).

The effect of static impurities in a two-dimensional quantum antiferromagnet has been studied. Creation of a vacancy in an antiferromagnetic lattice yields an impurity Hamiltonian whose x-y part maps to single impurity Anderson model whereas the z-part becomes the X-ray singularity problem. The model is solved where one obtains a bound state giving rise to δ-function density of states. The z-part of the interaction makes this peak asymmetric which follows a power law. It has been argued that the bound state corresponds to a local moment in the system giving rise to Curie-like contribution to the susceptibility. The implications of the present model in the substitutional Zn doped high-T_c oxides have been discussed.

Dynamic behavior of supercurrent in mesoscopic Josephson junction interacting with even coherent state (CS) and odd CS of nonclassical microwave with frequency ω₁ and classical radiation with frequency ω₂ is investigated. It is shown that the supercurrent through the junction has a dc component only for all rational values of ω₁/ω₂ (fractional Shapiro steps). It is also shown that the dynamic behavior of the supercurrent exhibits collapse and revival phenomenon and the revivals are dominated by the periodical superstructure. Dynamic behavior of supercurrent fluctuation is also studied and it is found that generally when the fluctuation is large, the supercurrent exhibits collapses and when the fluctuation is small, the supercurrent exhibits revivals.

The behavior of the mean photon number, photon number variance and field squeezing is investigated for the two two-level atoms prepared in a multiatom squeezed state coupled to the vacuum or thermal field. The value of superposition angle (θ) of the atomic states is found to affect the photon number variance as well as field squeezing. The bound on the sun-Poissonian field concerning the value of θ and input mean photon number is determined. One of the field quadrature is found to exhibit permanent squeezing for the vacuum input in a small range of the value of θ. It is shown that the input thermal photons degrade the sub-Poissonian character and spontaneous squeezing. However, a considerable amount of squeezing is obtained even in the presence of thermal photons.

Valence-band photoemission sspectra of Ni₃Al, Ni₃Ga and Ni₃In were measured with synchrotron radiation at photon energies around the Ni-3p core excitation threshold. The valence-band satellites are resonantly enhanced. The number of holes per Ni atom in the Ni-d band for Ni₃Al, Ni₃Ga and Ni₃In is estimated to be 0.37, 0.30 and 0.34, respectively. The self-energy correction due to the configuration interaction is 0.72, 0.71 and 0.72 eV, respectively, for Ni₃Al, Ni₃Ga and Ni₃In. The Fano parameters and the effective Coulomb interactions between two 3D holes for these intermetallic compounds are determined.