Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction

The spatial charge arrangement of a typical quasi-two-dimensional organic conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal stripe type structure, which was suggested by mean field theory, is established. We also find the charge disproportion above the metal-insulator transition temperature and a significant change in transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as a 2k_F charge density localization.Comment: 8 pages, 5 figures, 1 tabl

Electronic properties of correlated metals in the vicinity of a charge order transition: optical spectroscopy of α\alpha-(BEDT-TTF)2M_2MHg(SCN)4_4 (MM = NH4_4, Rb, Tl)

The infrared spectra of the quasi-two-dimensional organic conductors $\alpha$-(BEDT-TTF)$_2$$M$Hg(SCN)$_4$ ($M$ = NH$_4$, Rb, Tl) were measured in the range from 50 to 7000 \cm down to low temperatures in order to explore the influence of electronic correlations in quarter-filled metals. The interpretation of electronic spectra was confirmed by measurements of pressure dependant reflectance of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ at T=300 K. The signatures of charge order fluctuations become more pronounced when going from the NH$_4$ salt to Rb and further to Tl compounds. On reducing the temperature, the metallic character of the optical response in the NH$_4$ and Rb salts increases, and the effective mass diminishes. For the Tl compound, clear signatures of charge order are found albeit the metallic properties still dominate. From the temperature dependence of the electronic scattering rate the crossover temperature is estimated below which the coherent charge-carriers response sets in. The observations are in excellent agreement with recent theoretical predictions for a quarter-filled metallic system close to charge order

Charge Order with Structural Distortion in Organic Conductors: Comparison between \theta-(ET)2RbZn(SCN)4 and \alpha-(ET)2I3

Charge ordering with structural distortion in quasi-two-dimensional organic conductors \theta-(ET)2RbZn(SCN)4 (ET=BEDT-TTF) and \alpha-(ET)2I3 is investigated theoretically. By using the Hartree-Fock approximation for an extended Hubbard model which includes both on-site and intersite Coulomb interactions together with Peierls-type electron-lattice couplings, we examine the role of lattice degrees of freedom on charge order. It is found that the experimentally observed, horizontal charge order is stabilized by lattice distortion in both compounds. In particular, the lattice effect is crucial to the realization of the charge order in \theta-(ET)2RbZn(SCN)4, while the peculiar band structure whose symmetry is lower than that of \theta-(ET)2RbZn(SCN)4 in the metallic phase is also an important factor in \alpha-(ET)2I3 together with the lattice distortion. For \alpha-(ET)2I3, we obtain a phase transition from a charge-disproportionated metallic phase to the horizontal charge order with lattice modulations, which is consistent with the latest X-ray experimental result.Comment: 10 pages, 13 figures, to appear in J. Phys. Soc. Jpn. Vol. 77 (2008) No.

Using e-learning to engage unemployed rural women in aquaculture in Bangladesh to reduce poverty

Even though half of the population of Bangladesh is women, most of them are not working as paid employee or working as business owner. The main reason is that most of them are in rural area and unable to get proper education. This paper aims to develop a model that can assist different government organizations to assist those unemployed rural women to get involved in fisheries industries. This will help them to get proper information to get some income from whatever resources they have nearby for generate income from aquaculture.ACM International Conference Proceeding Serie

Charge disproportionation in the metallic state of α{\alpha} -(BEDT-TTF)2{_{2}}I3{_{3}}

$^{13}$C-NMR measurements have been carried out on the quasi two-dimensional organic conductor, $\alpha$-(BEDT-TTF)$_{2}$I$_{3}$. We measured the angular dependence of $^{13}$C-NMR spectrum at several temperatures above metal-insulator transition temperature, 135 K (=$T_{\rm MI,})$. We found that charge (spin) disproportionation already exists in the metallic state and gradually develops as temperature approaches to $T_{\rm MI}$. Key words. $^{13}$C-NMR, Charge disproportination.

Charge disproportionation, everywhere!

Charge disproportionation (CD) recently observed in many organic conductors is reviewed. CD is closely related to the charge ordering (CO) but is observed even when no long range CO is established. In a $\theta$-phase BEDT-TTF salt, (BEDT-TTF)$_{2}$RbZn(SCN)$_{4}$, an extremely slow dynamics of CD has been observed above $T_{\rm MI}$. A similar phenomenon is also observed in the Cs-analog, (BEDT-TTF)$_{2}$CsZn(SCN)$_{4}$. However, a spin-singlet ground state without CD is suggested in this salt at low temperatures. It is shown that $\alpha$-(BETS)$_{2}$I$_{3}$ exhibits CD at low temperatures, as in $\alpha$-(BET-TTF)$_{2}$I$_{3}$. Recently, an abnormal line broadening has been observed in $^{13}$C-NMR of (TMTSF)$_{2}$FSO$_{3}$ under pressure as well as in $^{77}$Se-NMR of $\lambda$-(BETS)$_{2}$FeCl$_{4}$ in a high field. We expect that both are very likely caused by a large CD among the organic molecular sites

Dark uncertainty

Standard uncertainties obtained by the GUM approach for a range of analytical methods are compared directly and indirectly with estimates of reproducibility standard deviation for the same methods. Results were obtained from both routine analysis and international key comparisons. A general tendency for the uncertainty to be substantially less than the reproducibility standard deviation was found