National Origin Differences in Wages and Hierarchical Positions - Evidence on French Full-Time Male Workers from a matched Employer-Employee Dataset

This paper estimates the differences in wages and hierarchical positions that can be attributed to national origin in France. Our data come from a matched employer-employee wage survey performed in 2002. The business survey provides very reliable wage data which are matched to many individual-level variables collected in a household survey. The sample of male full-time workers is decomposed into three sub-samples according to the parents' birthplace (France, North Africa and Southern Europe). The large number of executives in the sample allows us to perform a switching regression model of wage determination and occupational employment. We adapt and extend existing decomposition methods to this framework: while usual methods only take care of selection issues, we develop here a methodology which also properly takes into account composition effects due to differences in hierarchical positions when comparing mean wage gaps. Moreover the method we use only requires model estimation on the reference population and therefore yields more precise results when the sample size of the potentially discriminated group is small. Our results show no wage discrimination but a certain degree of occupational segregation yielding composition effects. Moreover, differences in the returns to some of the individual characteristics including higher diplomas might reveal mechanisms of statistical discrimination on the labor market.immigration, discrimination, wage gap, France

Theoretical Aspects of Charge Correlations in θ\theta-(BEDT-TTF)2X_2X

A review is given on the theoretical studies of charge correlations in $\theta$-(BEDT-TTF)$_2X$. Various studies show that within a purely electronic model on the $\theta$-type lattice with the on-site $U$ and the nearest neighbor $V_p$ and $V_c$ interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime $V_p< V_c$, $V_p\sim V_c$, and $V_p> V_c$, respectively. In the realistic parameter regime of $V_p\sim V_c$, there is a competition between c-axis three fold state and the diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron-lattice coupling, which tends to distort the lattice into the $\theta_d$-type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron-electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in $\theta$-(BEDT-TTF)$_2X$ may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed.Comment: 22 pages, 15 figures, to be published in Sci. Technol. Adv. Mater., Special Edition on Organic Conductor

Analysis of the Scanning Tunneling Microscopy Images of the Charge Density Wave Phase in Quasi-one-dimensional Rb0.3MoO3

The experimental STM images for the CDW phase of the blue bronze RbMoO3 have been successfully explained on the basis of first-principles DFT calculations. Although the density of states near the Fermi level strongly concentrates in two of the three types of Mo atoms Mo-II and Mo-III, the STM measurement mostly probes the contribution of the uppermost O atoms of the surface, associated with the Mo-IO6 octahedra. In addition, it is found that the surface concentration of Rb atoms plays a key role in determining the surface nesting vector and hence the periodicity of the CDW modulation. Significant experimental inhomogeneities of the b* surface component of the wavevector of the modulation, probed by STM, are reported. The calculated changes in the surface nesting vector are consistent with the observed experimental inhomogeneities.Comment: 4 pages 5 Figure

Dynamical singlets and correlation-assisted Peierls transition in VO2

A theory of the metal-insulator transition in vanadium dioxide from the high-temperature rutile to the low- temperature monoclinic phase is proposed on the basis of cluster dynamical mean field theory, in conjunction with the density functional scheme. The interplay of strong electronic Coulomb interactions and structural distortions, in particular the dimerization of vanadium atoms in the low temperature phase, plays a crucial role. We find that VO2 is not a conventional Mott insulator, but that the formation of dynamical V-V singlet pairs due to strong Coulomb correlations is necessary to trigger the opening of a Peierls gap.Comment: 5 page

Equilibrium Low Temperature Heat Capacity of the Spin Density Wave compound (TMTTF)2 Br: effect of a Magnetic Field

We have investigated the effect of the magnetic field (B) on the very low-temperature equilibrium heat capacity ceq of the quasi-1 D organic compound (TMTTF)2Br, characterized by a commensurate Spin Density Wave (SDW) ground state. Below 1K, ceq is dominated by a Schottky-like contribution, very sensitive to the experimental time scale, a property that we have previously measured in numerous DW compounds. Under applied field (in the range 0.2- 7 T), the equilibrium dynamics, and hence ceq extracted from the time constant, increases enormously. For B = 2-3 T, ceq varies like B2, in agreement with a magnetic Zeeman coupling. Another specific property, common to other Charge/Spin density wave (DW) compounds, is the occurrence of metastable branches in ceq, induced at very low temperature by the field exceeding a critical value. These effects are discussed within a generalization to SDWs in a magnetic field of the available Larkin-Ovchinnikov local model of strong pinning. A limitation of the model when compared to experiments is pointed out.Comment: 10 pages, 11 figure

A New Scenario on the Metal-Insulator Transition in VO2

The metal-insulator transition in VO2 was investigated using the three-band Hubbard model, in which the degeneracy of the 3d orbitals, the on-site Coulomb and exchange interactions, and the effects of lattice distortion were considered. A new scenario on the phase transition is proposed, where the increase in energy level separation among the t_2g orbitals caused by the lattice distortion triggers an abrupt change in the electronic configuration in doubly occupied sites from an S=1 Hund's coupling state to a spin S=0 state with much larger energy, and this strongly suppresses the charge fluctuation. Although the material is expected to be a Mott-Hubbard insulator in the insulating phase, the metal-to-insulator transition is not caused by an increase in relative strength of the Coulomb interaction against the electron hopping as in the usual Mott transition, but by the level splitting among the t_2g orbitals against the on-site exchange interaction. The metal-insulator transition in Ti2O3 can also be explained by the same scenario. Such a large change in the 3d orbital occupation at the phase transition can be detected by linear dichroic V 2p x-ray absorption measurements.Comment: 5 pages, 5 figures, to be published in J. Phys. Soc. Jpn. Vol. 72 No. 1

Collective Spin-Density-Wave Response Perpendicular to the Chains of the Quasi One-Dimensional Conductor (TMTSF)2PF6

Microwave experiments along all three directions of the spin-density-wave model compound (TMTSF)$_2$PF$_6$ reveal that the pinned mode resonance is present along the $a$ and $b^{\prime}$ axes. The collective transport is considered to be the fingerprint of the condensate. In contrast to common quasi one-dimensional models, the density wave also slides in the perpendicular $b^{\prime}$ direction. The collective response is absent along the least conducting $c^*$ direction.Comment: 3 pages, 4 figure

Electronic band structure and exchange coupling constants in ACr2X4 spinels

We present the results of band structure calculations for ACr2X4 (A=Zn, Cd, Hg and X=O, S, Se) spinels. Effective exchange coupling constants between Cr spins are determined by fitting the energy of spin spirals to a classical Heisenberg model. The calculations reproduce the change of the sign of the dominant nearest-neighbor exchange interaction J1 from antiferromagnetic in oxides to ferromagnetic in sulfides and selenides. It is verified that the ferromagnetic contribution to J1 is due to indirect hopping between Cr t2g and eg states via X p states. Antiferromagnetic coupling between 3-rd Cr neighbors is found to be important in all the ACr2X4 spinels studied, whereas other interactions are much weaker. The results are compared to predictions based on the Goodenough-Kanamori rules of superexchange.Comment: 15 pages, 10 figures, 3 table